Derby Cover Bolts
 

Does anyone know what size bolt for later big twin. Thanks
The heads (torx) are about gone. I'm thinking of going to a allen head or hex head.

I found these for the mean time.
Amazon has everything. Nice price.

Just get some more torx head bolts. Might as well get the correct sized wrench for them too. (T-27.)

Amazon? How about your local hardware store?

take one of the screws out of the derby cover. go to a local hardware store and ask them for some stainless aliens. simple as that.

I can't help with the size as I've never had the need to replace them however whether or not you go with hex or torx, always use the correct bit and use a speed handle to remove and install them.
The speed handle allows pressure to be put on the bolt/screw while being able to control how much torque is being applied.

I always use a 1/2" with a 3/8" adapter with bit due to the bigger 1/2" drive allows for more control.
However since you can get both the 3/8" and 1/2" for under $18 they both should be in everyone's tool box that wrenches their own bike.

https://www.harborfreight.com/38-in-...dle-62700.html
https://www.harborfreight.com/1-2-ha...dle-95992.html

For the Derby Cover, I'd use Buttonhead screws.

try 8-32 x 3/8, stainless button head

Put them in a drill and spin them against a rag with semi-chrome on it and polish them up

Pretty sure 1/4 -20 X 1/2in