This seal fits the vintage Girling 18-4 caliper, most famously used on the front of the Lola T70 and Ford GT40 Mk IV. The 18-4 had four 42.8mm (1.69") pistons. These seals are sold individually (4 required per caliper).
Note 1: These seals are for Girling 18/4 calipers only. They do not fit any other brand of calipers. Brakes are a critical safety component. We strongly recommend against trying to use these seals in other brands of calipers, even if the nominal piston size is the same. The results of brake system failure can have devastating effects!
Note 2: These seals get compressed to size when they are installed in the caliper bore. This is required for a tight seal. They will be slightly oversize (up to about 0.10" larger than the nominal size) when they are loose. They will not fit tight against the piston until they are installed in the caliper bore.