A fiberglass door can be drilled. The sheet metal screws provided with our closers are threaded completely to the head of the screw so will be secure in fiberglass. Use the ø3/16” drill bit called out in the instructions, or start with ø5/32” to be conservative. Drill one hole and insert the fasteners to insure it grips first before proceeding.
If unhappy with the results, buy ¼-20 Thru Bolts like the ones supplied with the 4061/62. But the head of the thru-bolt will be visible on the outside of the door.
