To replace all of them you will need to order a quantity of 3.

Must order quantity of 4 for complete set. 

Air compressor cylinder ring and o-ring kit. Includes compression ring, head o-ring, and valve plate o-ring.  This tends to be a high-wear part, especially if you are in a high-particulate environment. Pro Tip: Order the cylinder when buying this...

Compression nut and sleeve for 3/8" OD tubes.

Old Part Numbers: Z-AC-0032, AC-0032Valve plate comes with preinstalled valves and o-rings. Poor performance or air leaks out of the intake filter while the unit is running? This is probably the problem.

Old Part Numbers: 5130038-00, 5130024-001/4" OD brass nut and sleeve for bleeder (unloader) tube for air compressors.

There are several different air compressor cooling fan styles. Choose this if yours looks like this one. Replace if cracked or missing fins.