Caliper brakes have a center bolt 6 mm or 1/4" in diameter, which fits through a matching holes in the or of the frame. Traditionally, these bolts have been long enough to protrude all the way through, to be secured by a normal hex nut and associated . When a rear brake mounts to a curved surface on the brake bridge, you must use radiused washers (as shown in the photo below) to avoid crushing the brake bridge. If the mounting surface of the front brake is not radiused to fit the fork crown, a washer with a larger radius may be needed to support the brake and avoid unnecessary stress on the brake bolt. The fork crown is strong enough that it will not crush if the nut at the rear is attached using only a flat washer or lockwasher.
Most newer good-quality bicycles that use caliper brakes use recessed mounting to save weight and for a more elegant appearance. Calipers intended for recessed mounting have much shorter center bolts, which do not extend all the way through the crown/bridge. Frames/forks designed for recessed mounting have stepped holes...6 mm in front, 8 mm at the back. Instead of a conventional hex nut that takes a 10 mm wrench, a cylindrical nut is used, which is broached for a 5 mm Allen wrench.
Industrial Clutch Parts is pleased to introduce the new and expanded range of caliper brakes with innovative solutions for every requirement. Decades of experience combined with a continuous feedback with many different users and a careful analysis of their demands, has allowed us to develop a range of products that revolutionises the caliper brake concept with the introduction of many improvements and innovative technical solutions.