They are original. The name for the thread on them is called Acme. You will find that the front and back fenders use this type of thread and that you have a combination of screw heads as you found in the front and hex heads on the underside of the fenders and on the rear fenders. Roadster Factory has a set that they sell that contains the replacement screw and bolts plus the flat spire nut that they screw into. One set does a front or rear fender. There are other regular 1/4 inch fine thread bolts also on the front and rear fenders. Makes it interesting to keep track of what goes where when putting it back together.
By the way after redoing a TR3 with regular fine thread bolts and a TR4 with the Acme threads, I really like the Acme thread and spire nut. They do not sieze up with rust.
Good Luck in your adventure.
Charley Fitch
Maintenance Issues
