The bushing seals the oil galley, while the collar centers the rod and covers the hole. WIDE APPLICATION: Compatible with both SB and BB Chevy V8 & V6 engines. This tool supports various small and big block sizes, including popular options of 283, 307, 327, 350, 355, 383, 388, 396, 400, 402, 406, 427, 434, 454.