PURPOSE:To get rid of welding distortion, set each portion at proper strength and reduce the weight by clamping the front portions of right/left prongs which are forged or cast with a light alloy onto the right/left side faces on the rear portion of a center holder which is cast with a light alloy by means of a plurality of bolts. CONSTITUTION:A center holder 1 is cast by using a light alloy, a shaft cylinder 2 for making a support shaft installed on a frame pass through is provided on the front end thereof, and the inside is formed in a hollow portion by means of an inner ring. An installing face 4 having a cutout 3 connected to the hollow portion in its center is formed on each of the right/left side faces on the rear portion of the center holder 1. Right/left forks 6 are forged or cast with a light alloy and a mating face 8 having a projecting portion 7 in its center is formed on the inside front portion of each fork 6. By mating the mating faces 8 to the installing faces 4 of the center holder 1 while fitting the projecting portions 7 into the cutouts 3, the right/left prongs 6 are clampedly installed onto the center holder 1 with a plurality of bolts 11. Thereby, the wall thickness of the mating face 8 can be properly formed, to keep high accuracy while obtaining proper rigidity. The right/left forks 6 which are forged or cast can be formed in a proper wall thickness depending on a place, enabling the prongs to be light weight while keeping rigidity.
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