Industrial T-21 Seal Head Assembly Type T-21 for a 0.875-inch (7/8") shaft is a standard head component in Type 21 mechanical seals used on pumps and other rotating equipment. For the 0.875-inch shaft, bore (d) is 22.2 mm; the head outer diameter (D1) is 38.10 mm (1.50 in), and the D3 dimension for the T-21 variant is 33.4 mm (1.315 in). Mounting lengths are L1 = 23.80 mm (0.94 in) and L2 = 10.31 mm (0.41 in). In catalogs, this head is listed as Type T-21 and is commonly treated as equivalent to John Crane Type 21, designed to accompany compatible mating components in seal kits for 7/8" shafts in industrial service.
