"NHA A-20 HEATER; VENDOR ITEM IDENT IS COMPRESSION CLAMP, 2-INCH; SPECIFICATION CONTROL DRWG ITEM IDENT IS SPECIAL CLAMP; ITEM IS AN ASSEMBLY OF 3 BOLTS (10 MILLIMETERS), 1 WASHER, 1 NUT (10 MILLIMETERS), 1 GASKET, AND 2 PIECE CLAMP; ONE FACE OF CLAMP IS WELDED TO EXHAUST PIPE AND SECOND FACE IS SLIPPED OVER HEATER EXHAUST; SEAL IS MADE BY TIGHTENING BOLTS"