Adjustment Key, to fit A-dec 500®; Pkg of 4 For air & water adjustment on A-dec 500® blocks Package of 4 (A-dec® #38.1808.01) Key with O-Ring for air & water adjustment stems A-dec® and A-dec 500® are a registered trademark of A-dec, Inc. DCI has no affiliation with A-dec and A-dec has not authorized DCI replacement parts to be used on or in connection with A-dec® products.