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

New style filter assembly with 3/8" threads. Includes new style air filter, head, and o-ring. Note: Do NOT order if your head has 2 holes on the SAME side of the head. This head has 3/8" FPT threaded ports on both sides. If your head has a 3/8" port...

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

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