Newton, who makes our fuel fill caps
http://www.newton-equipment.com/

h
as a dry break cap that might fit, if anyone wanted to do a dry break fuel fill system. The width of the top flange is 3.7 in and our fuel caps top flange is 3.6 I believe. So it would probably fit.

Why do it? I dont know

http://www.newton-equipment.com/qfr1157.html