What screw/bolt size for gas filler door on 71 Coupe?

[nooilspots]

Found a gas filler door to replace my missing one and had it chrome painted.  Didn't have the fasteners to attach it to the body.  Cant seem to find any to fit the threaded inserts in the body to attach the door.  Parts book does not show the size.  Does anyone know what size bolt or screw fits?  Thanks in advance
George
Apple Valley CA
71 Coupe, previously 71 Sedan and 72 Coupe
46 years a Honda 600 owner