So you’ve tried everything you can think of and the damn nut is still frozen in place. Your next step: break the damn thing. Of course, it’d help if you could do so without jacking up the threads of whatever the hell it’s screwed to. That’s where nut splitters come in handy. You place ’em over the nut, then crank down slowly on the screw, applying mechanical advantage to drive an angled point into the nut, hopefully breaking it in half without mangling things up too bad.
I’ll be the first to admit that the only splitters like this I own are cheap-ass ones like the $12 models pictured above, available from Northern Tool. So maybe there’s some big advantage to owning a spend-tastic name-brand set. But damn if I can figure out what it’d be. They’re pretty clunky tools, and their purpose is simple enough that I suspect it’d take a lot of increased precision to make much functional difference in the tool. My recommendation — and please feel free to object in comments if you have some experience with these — is to pick up a cheap set, toss ’em in the toolbox, and be ready for the next time you don’t have any better option.
The pictured set claims to split nuts from 1/2″ to 7/8″. It also claims that it “won’t damage bolt threads,” which is a bit more iffy. (For what it’s worth, this isn’t a quality issue. They’re all a bit iffy.) Northern Tool also offers a 7/16″ to 3/4″ model, complete with a reverse-anvil setup where the screw drives a flat surface, pushing the nut into a splitter mounted on the other side of the bolt for around the same price.
2-Pc. Nut Splitter Set [Northern Tool]
Performance Tool Heavy Duty Nut Splitter, Model W88030 [Northern Tool]