To set the limitation of an installation place free and hence prevent a portion of parts from staying within an insert after mold release by forming a connection part to be ruptured readily between a flange including an opening provided on the tip end of a retaining part to be fitted with the insert and a projection having a male screw and situated in front of the flange.

The retaining part 2 is cylindrical member with a fitting hole 12 formed therein, and a flange 3 is formed of a larger opening 13 than the diameter of an insert attachment hole in order not to be interfered with an attachment of bolts or the like during use of the insert after mold release. In addition, at the tip end side of the flange 3, a projection 5 comes outward via a connection part 4, and the projection 5 includes a female 15 formed in its outer circumference. The connection part 4 for accomplishing connection between the flange 3 and the projection 5 comprises a plurality of connection pieces 14 arranged in petals, and thereby it is formed such that its cross-sectional area is made small to easily be ruptured by rendering the connection part with the flange 3 thin or narrow.