R21057 Air Stack Muffler Spacer Block Fits John Deere Tractor 620 630 720One New Aftermarket Replacement Air Stack Muffler Spacer Block Fits John Deere Tractors This aftermarket replacement muffler spacer block also known as an air cleaner stack riser Fits John Deere two cylinder row crop tractors. The block serves a dual purpose role in the exhaust and air intake system, functioning as either a muffler spacer or an air cleaner stack riser depending on application. On the 620 and 720 models, this part is used in the