The thread is an odd size. It is about a 10-36. The current 10-32 nuts won't fit. I bought two sets at the last gun show.
Rick I'm not sure what you are describing here but the 99 forend screw is absolutely a #8-40.
I was commenting on this...
I solved the problem a few years ago by rethreading a Model 70 type front sling swivel
