I have a couple vise swivel fasteners. The smaller one in the pic is stripped so it no longer tightens correctly. I have a set of these new (larger) ones but they are too large to fit the vise holes and swivel slots. I have a tap and die set and wondered can I die this larger one down without having to lathe off some material?

 

Nope, that's far too much of a difference for a die to cut, if it would even start on the die. And since the large one its threaded it would quickly cross thread and snap teeth in the die.

If you can take the T handle out, you might be able to chuck it in a drill or drill press and remove some material using a file, though a lathe would be better.

You could also cut off the threaded portion and weld on a bolt of the correct thread.

 

Love the welding idea. I'll most likely go that route