I've got a 65-4 that needs a new bolt, the threads are trashed on it. Is this a universal piece, or do I need to find a vintage part?

Go to the Smith and Wesson website and check there.  They will have the correct part.  You can also go to Numerich Arms and check their website also.  A -4 suffix revolver is not that old,

Thanks. I guess my assumption was that anything without the modern hammer style was obsolete in their mind.

Called Smith and was told that I could send it in for repair, but they wouldn't be able to mail me parts as they don't have access to obsolete part numbers... I'll buy from midwest and hopefully it fits.

I’m not sure if the new k frame mim bolt will work in your non mim k frame. I do know that the old style steel or stainless bolts work in the new style mim L and N frame guns. And I know the old steel j won’t work in the new j mim guns without retiming the rear of it where the hammer heel passes to function( back by the spring well /plunger area)

One thing to check is the pivot stud length. The new mim ones have a shorter pivot stud. Which makes you have to nudge the cylinder open.

Where the old style solid steel or stainless ones had the pivot stud fit to the gun so it flushes out with the blast shield when you push it forward. This lets the cylinder open without additional nudge on the cylinder side

Keep that in mind if you buy a used steel or stainless one. The pivot stud may be a little shorter than what your gun needs. Not a dead it the water thing though. You can tig a drop of metal onto the tip and reshape the od then just fit it to your frame to old fashioned way.

If you don’t find one anywhere else. Sometimes you can find the at USA guns and gear in Georgia

I actually found one on ebay. It does seem to catch on opening like you say. I'll have to play with it some more. Thanks for the tip!