Hi everyone! First post here. I have a couple of basses that have some string problems. The first one is a 2012 Fender Starcaster Reissue in black. When I replaced the stock strings with a set of Ernie Ball Slinky Cobalt 50-105's, it played perfectly, and I had no problems with them. Recently however, the A string broke on it, and I had to replace the entire set. I decided to downscale from 50's to 45's and after setting all of the strings down and playing them, they were getting annoying buzz on E A D, and up to the 2nd fret. I tried adjusting the truss rod, but that did no good whatsoever. My other bass is a 2002 Danelectro Rumor Bass in black. I had this bass taken to a lutherie after the nut chipped and started to come loose. When the lutherie was finished, I tried it out, and there was no buzz in the shop. However, after playing it a lot more, there was a buzz that started to gradually build the more I played it. Both this Danelectro and the Fender have D'Addario Nickel-wounds in 45-100 gauge. My last bass is a recently purchased Dean Edge 1 5-String bass in black. I'm thinking about changing them to DR Black Beauties in 45-125, but I'm afraid it'll end up as the exact same chapter as the Fender. So with all this in question, are nuts cut for a specific size of string, or is it the strings themselves? Thank you all so much for helping.