New aftermarket replacement air cylinder for Mack air assist clutch. Fits Mack part #21131322. Full stainless steel construction. 

This is the 3 Port air cylinder.  It has the vent port for the boot. It is not a direct replacement for Air Assist  Clutch cylinders with only 2 ports. The diameter of the rubber boot that covers the rod on the 2 port cylinder is to small to fit this 3 port cylinder. I have 2 port cylinders available as well. See my other listing for this part # by searching my store.