Crankcase Oil Fill Breather Vent Cap Replacement Generic Replacement crankcase oil fill breather vent cap. This is a generic replacement part for common air compressor pumps. This oil breather cap measures approximately 2-3/8" tall x 1" in diameter at the widest point, and has 3/8" straight threads (measures about 5/8" outside diameter). An O-ring seal helps keep this breather sealed without leaks. Specifications 2-3/8" Tall 1" Wide 3/8" Straight Threads (Measures about 5/8" Outside Diameter)