I'm working on a floating barn hanger at the Western Railway Museum. I need to put holes in my floating hanger that will allow you to bolt up a "conventional" barn hanger (if there is any such thing).

I've seen two types of barn hangers, one with parallel slots 4 3/4" apart, and another with forked ends that will accept a number of spacings including 4 3/4". The common denominator for both is that 1/2" bolts spaced 4 3/4" apart will bolt either one.

Are there any other types? Could I avail on folks to poke around in their parts bins and see what you have and if there's a different, significant size I should worry about?

The two types you mention sound like the Ohio Brass N-2 and H-3 hangers. (The H-3 has the slots) The N-2 has not been made in many years but the H-3 is still available. There are probably other kinds around but they would date from before World War 2 or earlier, when there were other trolley hardware manufacturers, or they would be mining equipment. I wouldn't worry about anything other than the two kinds you have.

Now a question on the kind with forks on the end (N-2?) Is the bolt supposed to float around somewhat free? On ours it seems to gimbal a bit, and turn about 3/4 of a turn and then hit a stop. Is that designed that way, or is that one broken internally?

H-3 barn hangers have the slots on the ends. I think you have one with a damaged insulator as the stud should not rotate or twist in the hanger. Check some of the others in your parts bin.