WHAT!!!? You don't have a collection of bolts of various sizes that you could fit in there to check? What kind of a Stovebolter are you anyway?
If it's a 216, then it would be 3/8 coarse thread. But a 216 only has two threaded holes and lugs for a hand crank, so that's not it. But if the engine is similar vintage, it's probably the same thread size.
What Otto said. They just charge you a deposit, refunded when you return it.
