So I recently came across a precision-style bass (not sure who built it) that was missing a nut. I bought a nut and sanded it down and installed it.

The issue I'm having isn't with the nut though, it's with the little round part on the headstock that adds tension to the top two strings. Not sure what the part is called, so here's a picture:


The groove on the bottom of that round piece that's supposed to fit the 2nd string is too narrow for the string. I'm using D'addario .045-.100 strings (the 2nd string is .065).

The problem I'm having is that these strings are wound narrower near the end (to make it easier to tune, I'm presuming). Whenever I'm putting the string on and winding it up, the spot where the string starts being wound at its full width hits that little notch. The pressure makes the string core snap and it just unwinds.

Now I only tried it once, but I don't want to waste a whole other pack of strings considering I know the same thing will happen again, and bass strings are expensive.

So what I want to know is, should I just get a replacement for that circular part that would fit the string better? Or should I buy a different type of strings that is wound at the same width all the way up the string? Or do you think I need to just be more careful with how I string the bass?

If you think this belongs in GB&C, I can delete this one and move it over there.
Only play what you hear. If you don’t hear anything, don’t play anything.
-Chick Corea
It's called a string retainer.
Damn it! Disable can't use disable to disable Disable's disable because disable's disable has already been disabled by Disable's disable!
Tighten the string without putting it under the retainer until it is just loose enough to slide it into the retainer grooves. By then, the beginning of the wind should be past the retainer. And don't forger to cut your strings down to about 10-13cm past the relevant post.
A bar string retainer will solve your problem, too. They cost about $4.00 and they require drilling two little holes for the screws. Any good repair tech can do it for you in five minutes.
"Maybe this world is another planet's hell?" - Aldous Huxley