If you installed three point seat belts, you’ll recognize the bigger center hole. The pop rivet gives it away! There is a threaded backing plate that is being held in place with that pop rivet until the seat belt in bolted in place.
I have no idea what the other two holes are for. Probably made before the seatbelts were installed.
EDIT: I like DES57’s guess, fire extinguisher mount, prior to the seatbelts!
Last edited by Phak1; Wed Jun 30 2021 01:08 PM.