For mounting sheet metal and fiberglass, quarter turn panel fasteners are the most practical fasteners requiring only one tool. Panel fasteners have been used in off-road racing for years due to their lightweight and durable design. Originally quarter turn fasteners came from the Military Aircraft industry. When they say #5 they are referring to the diameter of the button which is 5/16. Or if they say #6 they are referring to the diameter of the button which is 3/8. The length of the button is measured from the panel surface down to the bottom edge of the spring seat.
1-1/2 Inches Overall Height
1 Inches Bottom To Center Of Hole
For Countersunk 3/8" or 7/16" Buttons