PURPOSE: To prevent sockets from overlapping one over the other, when a spacer expander of undulate form in the radial direction is to be fitted in a ring groove and when a side rail is to be installed, and also to prevent drop of the strength, simplify the manufacturing processes, and suppress the cost through automating.
CONSTITUTION: A spacer expander of undulate form in the radial direction is provided with crests 2 and bottoms 3 alternately and with at least one socket, wherein a hole is bored in the bottom surface of the bottom part 3 adjacent to the socket, and an insert piece 4 having a body part and a protruding detention part formed in a single piece with the body part is engaged and fixed in the protruding detention part to the hole. This prevents overlapping of sockets of the spacer expander with one another, simplifies manufacture and mounting of the insert piece 4 without causing drop of the strength, accomplishes automation, and suppresses the manufacturing costs.
UMEZAWA KOJI
SAKURAI TAMIO
NIPPON PISTON RING CO LTD
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