AB1898R Fits John Deere A AO AOS AR B BO BR D G GP Brass Compression Relief PetcOne New Aftermarket Replacement Brass Compression Relief Petcock Fits John Deere Two Cylinder Tractors This brass compression relief petcock mounts directly to the cylinder head, allowing pressure to be released from the combustion chamber to ease hand cranking and cold starting on Fits John Deere two cylinder tractors. Constructed of C84400 valve brass with a 1 4 inch NPT pipe thread connection. Note: two petcocks are used per tractor this listing is