PURPOSE: To manufacture a groove insert easily at a low cost by providing the groove insert with a longitudinally extending spring arm made of plastic in the range of the wedge apex line of the insert, and providing a clamping portion at the resilient flexible free end of the spring arm, the clamping portion being supported at the bottom of a molded groove.

CONSTITUTION: A plastic base 1 has a fork range 1a and a hole formation range 1b. A longitudinal slit 4 is formed in the fork range 1a and serves to form a spring arm 5 extending in the longitudinal direction of the wedge apex line 1' of the plastic base 1, the spring arm having a clamping knob on the lower surface of its free end 5' for forming a clamping portion 6. The plastic base 1 inserted in a molded groove 7 in a molded rod 8 or the like is supported by the clamping knob against the bottom 7' of the molded groove under clamping action so as to fully prevent longitudinal movement of the plastic base 1 within the molded groove.