I just put a new plastic nut on my bass. The stock grooves are too small. Do I just use a regular file to widen the grooves? Or is there a certain type I should use for plastic?

Any file will work for plastic, it's more a question of the shape of the file.
If your nut has pre-cut slots that you want to widen, you could use a narrow needle file, or even a nail file. Try not to cut too deep and make the slot match the string. You don't want any gaps.
Stewmac and a bunch of other luthier supply stores have specific files for the job. They have them in particular string gauges so luckily you're not an 8 string guitar player haha.

so for example there is a 40 file , a 45 to whatever else you need string gauge wise.

for whatever reason if you go too far on one string or whatever remember baking soda and super glue are like concrete and it's a great drop fill that is as hard as concrete to try again. Just remember to tape off the fretboard and anywhere else the glue may drip on.
Last edited by Tallwood13 at Dec 25, 2014,
If it is indeed plastic, use the gauge of string and "saw" the slots a bit wider. You have to be careful to not go too deep. Best solution is take it to a tech, they might charge you $20 to re-slot the nut

^ the needle file idea is good if you don't mind spending a few bucks. You may even want to buy a set of files if you plan on pursuing working on and playing instruments
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