Stem, Drive Air Adjustment, to fit A-dec 300® and A-dec 500® Control Block Replacement stem for 300® & 500® control blocks (A-dec® #38.1785.01) A-dec®, A-dec 500® and A-dec 300® 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.