Looks like a Champion. Try to search for that complete air filter part number. The air filter will fit many compressors but that part number and the pump serial number should get you the information that you want.
Here is a screen shot of a video I took. Hope that helps.
Are you looking at buying? That Made in USA sticker looks like it’s a little bit newer. I don’t think mine had one. I will take a look, but I think there maybe another stamp on side of pump that shows age.
Thanks for all the help guys! I have it narrowed down to a R10 or R15. But I found that it has a 5HP motor, so i’m thinking it’s a R15 as Tool Tyrant says....