This coupler is used on 1986 and later MerCruiser 5.7L (350 ci) or 5.0L (305 ci) engine which is commonly called a "one-piece rear main seal" or "full seal". This coupler is frequently used when replacing a pre-1985, 350 ci or 305 ci with a 1986 or later, 5.7L (350 ci) or 5.0L (305 ci) engine. Replaces MerCruiser part# 14505A2 Replaces Sierra part# 18-2172 MR stamped coupling Used when replacing V6 or V8 2 piece rear main seal with 3-1/2 in. crankshaft bolt pattern to a newer 1 piece rear main seal engine with 3 in. bolt pattern.