Jim,
I am not sure I can answer your question, but I am sure the muffler bolts are metric. The best local spot to find some would be a local hobby shop (if you have one) since most RC cars now are metric and they will usually have a supply. The only issue will be if they have some that are long enough.

I think I still used 4/40 bolts on the mounting setup with planes like the Ringmaster Jr, and Sig Acromaster----basically that's what I have. 2-56 might be ok. I know I have some 2-56 blind nuts. Now that I think about it, I probably would use 2-56 simply because the maple wood on your 1/2a Pathfinder might be too narrow for 4-40 size bolts. Might want to consider using some 2-56 washers under the bolt head to spread the load on the engine lugs.

Well I went and grabbed my FP10, which I think is the same as the TT10. The muffler bolts are 2.5mm diameter (0.098") and ~23mm long. I think the thread is 0.5 mm pitch (1 turn=1/2 mm).

I see from my metric bolt chart that a standard bolt is a 2.5mm x 0.45mm pitch. That is probably it. The closest domestic bolt would be a 3-56, pretty darn close actually--if you can find one, and that is at least an inch long. I bet it would work fine.

Hello Alan, Not trying to know any holes here... I'm in NYC but my chance of getting around is MOM dependent. She has good days I get a quick walk in the local area and she has bad days. I don't get out and spend the day trying to keep her calm. about 2-3 months ago I made it to the local ace hardware. That was a train trip to columbus ciricle and then walked 2 miles uptown to about 90 th street. And they weren't like MY local ace hardware in ca. about 50% MORE EXPENSIVE AND DID NOT CARRY DRILLS BY THEIR NUMBERS.