SSP-7821 .563-18 UNF Hex Nut

The SSP-7821 is a genuine OEM replacement part to secure the air compressor air tube to the oil-free air compressor pump's head.

Many air compressor models manufactured by companies such as Craftsman, Black and Decker, DeVilbiss, DeWALT, Porter Cable, and more used the SSP-7821. 

When replacing, it's also recommended to replace the silicone sleeve or o-ring, depending on your model.