Replacement gas cap

[RWilson2526]

Well I left gas cap on the gunwhale of the boat when filling up this morning and noticed is was gone out on the water. Gas station was only 3 blocks from the ramp so I retraced my steps afterwards but no deal.

Anybody ever have to replace just the cap? I know I can get the whole fitting with cap and all but if anyone knows the thread size and particular info to just get a new screw on cap will save me some research and time.