PURPOSE: To improve strength of the hole portion for mounting on a base substance by forming a hole portion by means of using an insert fitting, which is for demarcating the hole diameter of the mounting hole portion on a synthetic resins bracket, and by means of embedding into a synthetic resins the insert fitting with its circumference enclosed with a reinforcement fiber material.

CONSTITUTION: A flange 8 is formed on both sides of a bracket 1, which holds in between a cylindric bushing type vibration-proof device A with a rubber elastic body 5 bridging between a metal inner cylinder 3 and a metal outer cylinder 4, and a mounting hole 9 to mount it on a base substance is provided on the flange 8 with the size of the mounting hole demarcated by an insert fitting 10. A glass fiber cloth 14, having a hole 13 in its center and overlapped and embedded between both edge flanges 11, 12 of the fitting 10, is installed in a bracket forming die in a specified position and, thereafter, a material containing sythetic resins forming material is injected into the die. This bracket 1 is formed with a polyamide resins (6,6-nylon).