Inventors : Kazuyoshi TAKANO and Jimmy Jun-Fu CHANG

Cross Reference to Related Applications;

[1] The present application claims priority to U.S. provisional application serial number 62/644,776 and filed on 3/19/2018 and titled "Removal Tool for a Plural of Micro Optical Connectors From An Adapter Interface." The provisional application is incorporated into this present non-provisional application.

Field of the Invention:

[2] The present disclosure relates generally to ultra small form factor optical connectors, termed "micro optical connectors," and related connections within adapters and optical transceivers .

Background:

[3] The prevalence of the Internet has led to unprecedented growth in communication networks . Consumer demand for service and increased competition has caused network providers to continuously find ways to improve quality of service while reducing cost.

[4] Certain solutions have included deployment of high-density interconnect panels. High-density interconnect panels may be designed to consolidate the increasing volume of interconnections necessary to support the fast-growing networks into a compacted form factor, thereby increasing quality of service and decreasing costs such as floor space and support overhead. However, room for improvement in the area of data centers, specifically as it relates to fiber optic connects, still exists. For example, manufacturers of connectors and adapters are always looking to reduce the size of the devices, while increasing ease of deployment, robustness, and modifiability after deployment. In particular, more optical connectors may need to be accommodated in the same footprint previously used for a smaller number of connectors in order to provide backward compatibility with existing data center equipment. For example, one current footprint is known as the small form- factor pluggable transceiver footprint (SFP) . This footprint currently accommodates two LC-type ferrule optical connections. However, it may be desirable to accommodate four optical connections (two duplex connections of transmit/receive) within the same footprint. Another current footprint is the quad small form-factor pluggable (QSFP) transceiver footprint. This footprint currently accommodates four LC-type ferrule optical connections. However, it may be desirable to accommodate eight optical connections of LC-type ferrules (four duplex connections of transmit/receive) within the same footprint .

[5] In communication networks, such as data centers and switching networks, numerous interconnections between mating connectors may be compacted into high-density panels. Panel and connector producers may optimize for such high densities by shrinking the connector size and/or the spacing between adjacent connectors on the panel. While both approaches may be effective to increase the panel connector density, shrinking the connector size and/or spacing may also increase the support cost and diminish the quality of service. [6] In a high-density panel configuration, adj acent connectors and cable assemblies may obstruct access to the individual release mechanisms . Such physical obstructions may impede the ability of an operator to minimize the stresses applied to the cables and the connectors. For example, these stresses may be applied when the user reaches into a dense group of connectors and pushes aside surrounding optical fibers and connectors to access an individual connector release mechanism with his/her thumb and forefinger. Overstressing the cables and connectors may produce latent defects, compromise the integrity and/or reliability of the terminations, and potentially cause serious disruptions to network performance .

[7] While an operator may attempt to use a tool, such as a screwdriver, to reach into a dense group of connectors and activate a release mechanism, adjacent cables and connectors may obstruct the operator's line of sight, making it difficult to guide the tool to the release mechanism without pushing aside the adjacent cables. Moreover, even when the operator has a clear line of sight, guiding the tool to the release mechanism may be a time-consuming process. Thus, using a tool may not be effective at reducing support time and increasing the quality of service.

Brief Description of the Drawings;

[8] FIG. 1 is a perspective top view of a group of micro connectors with a push/pull tab similar to the micro connector of FIG. 2.

t9] FIG. 2 is a perspective view of a micro connector according to the present invention. [10] FIG. 3 is a perspective view of a group of micro connectors of FIG. 1 with a removal tool attached at a distal end of the micro connectors pull/push tab.

[11] FIG. 4.1 is perspective top view of a group of micro connectors similar to FIG. 1 just prior to the insertion of a removal tool shown fully inserted at FIG. 4.3.

[12] FIG. 4.2 is a perspective view of a removal tool according to a second embodiment of the present invention.

[13] FIG. 4.3 is a perspective top view of the removal tool of FIG. 4.2 inserted at a distal end of the group of micro connectors as shown in FIG. 4.1

[14] FIG. 5 is a top perspective view of a group of micro connectors with an alternative push/pull tab configured to accept the removal tool of FIG. 4.2.

[153 FIG. 6 is a cut away view of the removal tool of FIG. 3 inserted at a distal end of a push/pull tab of a micro connector.

[16] FIG. 7 is an isometric view of a third embodiment of a removal tool attached at distal end of a push/pull tab of a group of micro connectors.

[17] FIG. 8 is a cross-section view of the removal tool of FIG. 7.

[18] FIG. 9 is an isometric perspective view of fourth embodiment of a removal tool attached to a distal end of a push/pull tab of a group of micro connectors.

[19] FIG. 10 is a cross-section view of the removal tool of FIG. 9, the removal tool is in an unlocked position attached to a distal end of a push/pull tab of a micro connector of the present invention.

[20] FIG. 11 is a cross-section view of the removal tool of FIG. 9 in a locked position attached to a distal end of a push/pull tab of a micro connector for removal thereof according to the present invention.

[21] FIG. 12 is an isometric view of fifth embodiment of a removal tool attached to a distal end of a push/pull tab of a group of micro connectors .

[22] FIG. 13 is a cross-section of the removal tool just prior to an unlocked position to unlock a micro connector with the removal tool of FIG. 12.

[23] FIG. 14 is a cross-section of the removal tool locking a micro connector using the removal tool of FIG. 12.

[24] FIG. 15 is a perspective view of the removal tool of FIG. 12 with removal tool release arms in an asymmetric layout .

[25] FIG. 16 is a perspective view of a plural of micro connectors without a removal tool of FIG. 18 attached at a distal end of the connectors.

[26] FIG. 17 is a perspective view of the removal tool of FIG. 18 inserted at a distal end of a group of micro connectors .

[27] FIG. 18 is an isometric view of sixth embodiment of a removal tool .

[28] FIG. 19 is a cross section of the removal tool inserted into recesses at a distal end of the micro connectors of FIG. 17.

[29] FIG. 20.1 is a perspective view of seventh embodiment of a removal tool .

[30] FIG. 20.2 is a perspective view of the removal tool of FIG. 20.1 attached to a distal end of a micro connector.

[31] FIG. 20.3 is a perspective view of a group of micro connectors including the removal tool of FIG. 20.1 attached as shown in FIG. 20.2. Detailed Description;

[32] This disclosure is not limited to the particular systems, devices and methods described, as these may vary. The terminology used in the description is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope.

[33] As used in this document, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise.

[34] The following terms shall have, for the purposes of this application, the respective meanings set forth below.

[35] A connector, as used herein, refers to a device and/or components thereof that connects a first module or cable to a second module or cable. The connector may be configured for fiber optic transmission or electrical signal transmission. The connector may be any suitable type now known or later developed, such as, for example, a ferrule connector (FC) , a fiber distributed data interface (FDDI) connector, an LC connector, a mechanical transfer (MT) connector, a square connector (SC) connector, an SC duplex connector, or a straight tip (ST) connector. The connector may generally be defined by a connector housing body. In some embodiments, the housing body may incorporate any or all of the components described herein.

[36] A "fiber optic cable" or an "optical cable" refers to a cable containing one or more optical fibers for conducting optical signals in beams of light. The optical fibers can be constructed from any suitable transparent material, including glass, fiberglass, and plastic. The cable can include a jacket or sheathing material surrounding the optical fibers . In addition, the cable can be connected to a connector on one end or on both ends of the cable .

[37] Various embodiments described herein generally provide a remote release mechanism such that a user can remove cable assembly connectors that are closely spaced together on a high density panel without damaging surrounding connectors, accidentally disconnecting surrounding connectors, disrupting transmissions through surrounding connectors, and/or the like. Various embodiments also provide narrow pitch LC duplex connectors and narrow width multi-fiber connectors, for use, for example, with future narrow pitch LC SFPs and future narrow width SFPs . The remote release mechanisms allow use of the narrow pitch LC duplex connectors and narrow width multi -fiber connectors in dense arrays of narrow pitch LC SFPs and narrow width multi-fiber SFPs .

[38] FIG. 1 show a plural 7600 of micro connectors 3700 prior to insertion into an adapter (not shown) . FIG. 2 shows a single micro connector 3700 configured to accept a removal tool at release recess 4473. Fiber optic ferrules (3702a, 3702b) defined a proximal end of micro connector 3700. Adapter latch hook flexes into recess 3702c during insertion of micro connector 3700 into an adapter receptacle (not shown). Applicant pending patent application U.S. Pat. No. 20190018209A1 "Ultra-Small Form Factor Optical Connectors", Inventor Takano, discloses adapter and micro connector latching such as at FIG. 23A.

[39] FIG. 3 depicts a first embodiment of removal tool 7870 attached to a distal end of a plural of micro connector 3700a-3700d forming a removal tool assembly 7600. Removal tool 7870 further comprises a plural of release arms 7875a- 7875d for each micro connector (3700, 5300) group together. In operation, a user would pull up in the direction of arrow "A" a release arm 7875, then pull in direction of arrow "B" to remove one or more micro connector for which the arm is not activated or pulled up.

[40] Referring to FIGS . 4.1 to 4.3, a second embodiment of removal tool 7970 is shown. Referring to FIG. 4.1, tool 7970 further comprises guide block 7976 that is configured to engage and be inserted into a corresponding opening 5376 located at a distal end of a push/pull tab 5310 of micro connector 5300, located at FIG. 4.1. Connector 5300a further comprises push/pull tab release 5310a. Connector 5300b comprises push/pull tab 5310b. Connector 5300c comprises push/pull tab 5310c.

[41] Referring to FIG. 4.2, removal tool 7970 contains a plural of release arms 7975 in operation that get pulled up when removing the tool, as described below. Pulling up on one or more release arms prior to displacing the tool in the distal direction, the corresponding micro connector is retained or not removed from its corresponding adapter receptacle. FIG. 20.3 depicts a plural of micro connectors secured within an adapter receptacle. FIG. 4.1 depicts a release recess 4473 for each micro connector. For example, release recess 4473 is for micro connector 5300a. Referring to FIG. 4.1 and FIG. 4.2, removal tool 7975 inserted at the distal end of a plural of micro connector 5300 is as shown in the direction of arrow "C".

[42] Referring to FIG. 4.3, upon insertion each release arm 7975a-7975d engages a release recess 4473a-4473d (refer to FIG. 4.1) , and upon removing the tool in the direction of arrow "B" all micro connectors would be removed from an adapter (not shown) . Pulling up one or more release arms 7975 (also shown in FIG. 4.2 7975a-7975d) ) in the direction of arrow "A" and removing the tool in the direction of arrow "B", the micro connectors corresponding to the pulled up release arm, those micro connectors would remain in its corresponding adapter receptacle (not shown) .

[43] Referring to FIG. 5, a plural of micro connectors 8000 with an alternative pull/push tab release 8010. Push/pull release 8010a comprises handle 8010a.1 at the distal end of the micro connector 8000a. Release tool 7970 can be configured to accept a second handle type 8010a.1 without departing from the scope of the invention.

[44] Referring to FIG. 6, removal tool 8170 is shown locked onto a distal end of a push/pull release 8110a, forming removal tool assembly 8100, when release arm 8175a protrusion 8175a.1 engages an opening or recess 8173a in push/pull tab release 8110a. Pulling release arm rearward in this FIG. 6 in the direction of arrow "A", the micro connector is removed from its corresponding adapter receptacle.

[45] Referring to FIG. 6, to disengage the lock formed between the protrusion 8175a.1 and recess 8173a, release arm 8175a is lifted up in direction of "U" . Then when removal tool 8170 is pulled rearward, in the direction of arrow "A", the micro connector (3700 or 5300) is not removed from an adapter (not shown). That is protrusion 8175a.1 is removed from recess 8173a, and upon a distal or rearward pull of removal tool 8170, micro connector (3700a, 5300a or 8100a) is retained in adapter receptacle (not shown) by an adapter latch (not shown) within micro connector recess at a proximal end of the micro connector. This securing of micro connector into adapter via a latch is well known in the art.

[46] FIG. 7 depicts a third embodiment 7200 of removal tool 8270 connected at a distal end of a plural of micro connector 3700a-3700d. Removal tool 8270 further comprises release arms 8275a-8275d, one release arm for each micro connector ganged together within the housing 8270a of removal tool 8270.

[47] FIG. 8 depicts a cross-section view of micro connector 3700a, as shown in removal tool assembly 7200, which is a plural of micro connectors ganged or grouped together with removal tool 8270. At FIG. 8, removal tool 8270 is shown in a locked position at the distal end of micro connector 3700 or 5300. FIG. 8 is the cross-section of the third embodiment of removal tool 8270. In FIG. 6, locking arm protrusion is deflected in the upward direction "U" and in FIG. 8, release arm locking protrusion 8375c.1 is deflect downward of "D" direction. In both cases, release arm unlocks and the micro connector is not removed from its adapter receptacle when the removal tool is displaced distally

[48] Referring to FIG. 8, removal tool 8270 further comprises release arm 8375 at a first end, recess locking protrusion 8375a.1 at a second end and a release arm locking protrusion 8375c.1 along a first or second side of its corresponding release arm. Recess locking protrusion 8375a.1 engages a corresponding opening or recess 8373a located at a distal end of the push/pull tab on connector 3700a to lock micro connector 3700 within removal tool 8270 housing. Removal tool 8270 housing further comprises recess 8370a.1 configured to accept release arm locking protrusion 8375c.1. Upon insertion of removal tool 8270 onto the distal end of the plural of micro connectors (3700, 5300) as depicting at removal tool assembly 7200, removal tool 8270 locks via release arm protrusion 8375c.1 into opening 8370a.1 and release locking protrusion 8375a.1 in recess 8373a (also shown at FIG. 4.1 as recess 4473). When depressing the corresponding connector release arm 8375 in the direction of the arrow "D", locking protrusion 8375c.1 is moved out of recess 8370a.1, and removal tool 8270 is pulled rearward or in direction of arrow "R" . When a release arm is depressed, "D", its corresponding micro connector is retained in an adapter (not shown) , while the remaining micro connectors of the plural of micro connectors are removed from an adapter receptacle (not shown) upon moving removal tool 8270 in the direction of arrow "R". FIG. 8 depicts release arm 8375 in locked position that upon displacing removal tool distally, the corresponding micro connector, in-line with release arm 8375, is removed from its adapter receptacle.

[493 FIG. 9 depicts a fourth embodiment of a removal tool 9470 securing a plural micro connectors 3700a-d, housing 9470a further gangs or groups release arms 9475a-9475d corresponding to the number of micro connectors 3700a-3700d secured within the removal tool housing 9470a. It is understood the plural of micro connectors can be micro connector 3700, 5300 or 8000 without departing from the scope of the invention. FIG. 9 is in an unlocked position. Displacing removal tool 9470a distally (or an individual release arm distally) , none of the micro connectors are removed from their corresponding adapter receptacle.

[50] Referring to FIGS. 10 to 11, the operation of removal tool 9470 is disclosed. In FIG. 10, release arm 9475a is in an unlocked position with its corresponding release arm locking protrusion 9475c.1 disengaged from a corresponding flexible latch 9470d.l (refer to FIG. 11) formed as part of removal tool 9470. Displacing removal tool 9470 in a distal direction, the micro connector is retained in its adapter receptacle .

[51] Referring to FIG. 11 , release arm 9475a ( in a locked position) is moved to a proximal end or in the direction of arrow "A" (refer to FIG. 10) . As removal tool is moved proximally, release arm locking protrusion 9475c.1 engages flexible latch 9470d.1 integrated as part of housing 9470a of removal tool 9470. Flexible latch 9470d.1 is displaced into recess 8573 located at a distal end of pull/push tab release 8510 attached to micro connector 5300 or 3700. FIG. 11 depicts a locked position of removal tool 9470. Pulling removal tool 9475 distally or pulling it rearward, one or more micro connectors are removed or unlatched from an adapter (not shown) . Referring to FIG. 10, the release arm is in an unlocked position, and upon removing tool 9470, the one or more micro connectors are not removed or remain latched in an adapter (not shown) in the unlocked position of release arm 9475a (FIG. 10) .

[52 ] Without departing from the scope of the invention, one or more micro connectors of a plural of micro connectors, with any of the removal tools, the release arm may be positioned in an unlocked or locked configuration, and upon pulling the removal tool rearward, the corresponding micro connector that corresponds to a release arm is not removed or removed from an adapter.

[ 53 ] Referring to FIGS. 12 - 15, a fifth embodiment of a removal tool to remove one or more micro connectors from an adapter (not shown) is disclosed. FIG. 12 depicts a fully assembled plural of micro connectors 3700 secured within removal tool 8770 housing 8770a, as removal tool assembly 8700. A plural of release arms 8775a-8775d each with a release arm protrusion 8775b is depicted in assembly 8700. Still referring to FIG. 12, plural of micro connectors 3700 or micro connectors 5300, without departing from the scope of the invention, have attached at the distal end of pull/push tab 8710 removal tool 8770. Removal tool 8770 further comprises housing 8770a, one or more release arms 8775a- 8775d, and each release arm further comprises one or more release arm locking protrusion 8775b.

[54] Referring to FIG. 12, each release arm 8775a-8775d corresponds to micro connector 3700a-3700d more specifically the removal tool is configured to attach to and integrate with pull/push tab 8710 of its corresponding micro connector 3700. Each release arm 8775a- 8775d operates independent of the other to retain or remove its corresponding micro connector from an adapter receptacle. This release action occurs upon the distal movement of the removal tool . In operation, each release arm 8775a- 8775d is placed in a locked or unlocked position relative to its corresponding micro connector. FIG. 12 depicts all release arms in a locked position. In a locked position of a release arm, upon a distal movement of removal tool, the corresponding micro connector to the locked release arm, this corresponding micro connector is removed from its corresponding adapter receptacle. Distal movement is away from the proximal end of the micro connector. The proximal end of the micro connector is defined as the end with fiber ferrules showing.

[55] FIG. 13 depicts removal tool release arm 8775a, of FIG. 12, pushed in toward the proximal end of the micro connector and then down in direction of arrow "D" to arm release unlocking position. This will result in the corresponding micro connector not being removed from its adapter receptacle. Unlocking is relative the micro connector secured within an adapter. The locked and unlocked position is relative to the adapter receptacle. In locked position (refer to FIG. 14) , and moving the removal tool distally, a micro connector is removed. FIG. 13 depicts retaining the micro connector within its adapter receptacle. The micro connector retained or released is the micro connector corresponding to the release arm on the longitudinal axis of the micro connector, as depicted in FIG. 12.

[56] Referring to FIG. 13 , as release arm 8775a is being depressed downward in "D". Once fully depressed, release arm locking protrusion 8770c .1 moves out of recess 8773a or beyond wall 8773a.1, which allows the release arm 8775a secured within the removal tool housing, to be pulled rearward. Upon rearward movement, in direction of arrow "R", of removal tool 8770, the micro connector corresponding to its release arm, this micro connector is not removed from an adapter (not shown) , or the micro connector is retained in its adapter receptacle or locked therein.

[57] FIG. 14 depicts release arm 8775 in a locked position at a distal end of the pull/push tab 8710 of corresponding micro connector 3700. In a locked position, upon pulling release arm 8775 rearward or in the arrow direction "R", because release arm 8775 is secured within a first recess 8775e.l at a distal end of its corresponding micro connector via release arm latch 8775d.l, the removal in direction of "R" will remove the micro connector from an adapter (not shown). Locking arm 8770c protrusion 8770c.1 is retained within recess 8773 during the movement in direction of "R", thereby releasing micro connector from adapter receptacle. Locking arm 8770c is interconnected with release arm 8775 via latch 8775d.l. Removal tool housing 8770a further comprises a separate release arm 8775, a first locking recess 8775e.l and a second locking recess 8775e.2, and release arm latch 8775d.1. Release arm latch 8775d.l moves from first locking recess 8775e.l to a second locking recess 8775e.2. The operation of release arm latch 8775d.l and locking recesses (8775e.l, 8775e.2) retain release arm 8775 in a locked (refer to FIG. 14) or unlocked (refer to FIG. 13) position of the micro connector relative to its corresponding adapter receptacle. In a locked position for the release arm, the micro connector is removed from its corresponding adapter receptacle upon a distal movement of the removal tool.

[58] Upon full insertion of the removal tool over a distal end of a micro connector pull/push tab 8710 (as depicted in FIG. 12) , latch 8775d is locked into first locking recess 8775e.l. This prevents further rearward movement of release arm 8775 from the removal tool 8770 to prevent the removal tool from being inactive. Release arm 8775 further comprises release arm protrusion 8775b, where protrusion 8775d causes locking arm 8770c locking protrusion 8770c.1 to move out of recess 8773 when release arm 8775 is move forward or in proximal direction, as depicted in FIG. 13.

[59] Referring to FIG. 14, as release arm 8775 is moved forward, the latch 8775d moves out of first locking recess 8775e.l to second locking recess 8775e.2, and in this position, release arm is in an unlocked position. In an unlocked position (refer to FIG. 13), the micro connector is not removed from an adapter (not shown) . In a locked position, FIG. 14, the release arm will remove the micro connector from the adapter (not shown) when release tool 8770 is displaced in the direction of arrow "R". Still referring to FIG. 14, as release arm 8775 is moved proximal, release arm locking protrusion 8775d flexes out in direction of "F", as release arm locking protrusion is moved proximally into removal tool housing 8770a as depicted in FIG. 13.

[60] FIG. 14 includes locking arm 8770c. Locking arm 8770c is integrated to removal tool housing 8770a. Locking arm 8770c is also connected to release arm 8775 by latch 8775d. In operation one pulls or pushes release arm 8775a which moves locking arm 8770c protrusion 8770c .1 in or out of recess 8773a.

[61] FIG. 15 depicts a plural of micro connector 3700 or 5300 comprising a plural of release arms 8875 configured asymmetric or offset for easy access . Offset release arm 8875a is shorter or nearer removal tool 8870 than release arm 8875d. The operation of removal tool 8870 in FIG. 15 is the same as removal tool 8770 as described in FIG. 13 and FIG. 14.

[62] FIGS. 16-19 depict a fifth embodiment of a removal tool and its operation. FIG. 16 depicts removal tool assembly 8900 having a plural of micro connectors 3700 with pull/push tab 8910 and recess 8973 at the distal end of tab 8910a- 9810d. Each recess 8973a has pair of walls (8973a.1, 8973a.2) .

[63] FIG. 17 depicts plural of micro connectors 3700 with removal tool 8975 of FIG. 18 installed into the recesses 8973a-8973d of the plural of micro connectors of FIG. 16.

[64] FIG. 18 depicts a sixth embodiment of removal tool 8975 having body 8975a, plural of a pair of flexible arm 8975f.l and 8975f.2 sets, and each arm has a corresponding chamfer 8975g.l and 8975g.2. Set of flexible arms (8975f.l, 8975f .2 } is inserted into recess 8973 of corresponding push/pull tab 8910. Chamfers 8975g.l, 8975g.2 aids in the insertion of the arms into the recess, and the orientation of the chamfer, as shown, ensures arm 8975f flexes inward as the chamfers engage with push/pull tab recess walls 8973a.1, 8973a.2 upon insertion of removal tool 8975 into recesses 8973a-8973d. Once the arm pair is through the recess, a shelf pair 8975s.1, 8975s.2 secures the removal tool within recess 8973a. Shelf 8975s.1 expands under wall 8975f.l and shelf 8975s.2 expands under wall 8975f.2, thereby preventing flexible arms from being removed from its corresponding recess at the distal end of the fiber optic connector.

[65] FIG. 19 depicts a cross section of removal tool 8975 inserted into recesses 8973a-8973d of the plural of push/pull tab 8910a-d. Without departing from the scope of the invention, the tool 8975 may have two or more arm sets side by side or spaced apart for insertion in any number of recess of a plural of micro connectors.

[66] FIGS. 20.1 to 20.3 depict a seventh embodiment of a removal tool. FIG. 20.1 depicts removal tool 9075 extends the length of pull/push tab 9010 as shown in FIG. 20.2. Removal tool 9075 or extender further comprises a pair of extender arms 9Q75h each with wing 9075j . Referring to FIG. 20.2, extender arms 9075h snap into recess 9073 (refer to FIG. 20.3) at the distal end of push/pull tab 9010. The extender length may be varied to accommodate an asymmetric configuration similar to FIG. 15. Referring to FIG. 20.3, single tool 9075 may be installed at a distal end of one of the plural of micro connectors to remove that individual micro connector.

[67] In the above detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be used, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. An element 3700 refers to the item such as a connector while 3700a, 3700b, 3700c or 3700d refers to a plural of the individual item.