Quick read: The argument over bone versus Tusq versus brass is mostly settled before it starts, because a slot cut wrong undoes whatever the material gave you. The slot needs to be a couple thousandths wider than the string, rounded at the bottom to cradle it, and angled down toward the tuners so only the front edge of the nut touches. StewMac and Hosco both cut that slot. StewMac is the US standard and a hair finer on the narrowest strings. Hosco is widely held to be the same tool for about half the price, if you can wait on shipping. Pick by availability and budget, not by which one is "better." Get the slot right and the open string rings as clear as a fretted note and comes back to pitch with no ping.
People spend a week deciding between a bone nut and a Tusq nut. Then they cut the slot with the wrong file and wonder why the open string still pings and the high E goes sharp after a bend. The material was never the problem. The slot was.
A nut does one job. It holds the string at the right height and lets it slide when you tune. Everything you hear blamed on the nut material is usually the slot. So before you order another blank, learn what a good slot looks like and what cuts one.
What a Good Slot Actually Looks Like
A slot is not a notch. It is a shaped channel.
The bottom is rounded to the shape of the string, so the string sits in a cradle instead of on a point. The width is a couple thousandths over the string diameter, so the string slides instead of grips. The slot angles down toward the tuners, so the string breaks over the front edge of the nut and nowhere else. That front edge is the witness point. It is the only part of the nut that should touch the string.
Get those three things right and the string returns to pitch every time. Get any one of them wrong and you chase tuning ghosts forever.
The V-slot is the killer. A triangle file or a hacksaw blade cuts a V with a pointed bottom. The string sits on the point, pinches against both walls, and hangs up when you tune. That is the ping. That is the sharp note after a bend. A gauged nut file cuts the rounded slot the string needs. That is the whole reason these files exist.
StewMac Files: The US Standard
StewMac sells gauged nut files made for guitar work. Each file is ground to a specific width and cuts a rounded bottom at that gauge. They come as singles or as sets, and you can have them on the bench in two days. In the US, this is the file most techs reach for. It is the standard for a reason.
Where the StewMac files earn their keep is the narrow end. On a plain high E, where the slot is a few thousandths wide and there is no room for error, the StewMac grind is precise and clean. Fine work on a thin string is where you feel the quality. A six-file set runs around ninety dollars. That is real money for a hobby, but it is a buy-once tool, and the availability alone is worth something when you need a file this week and not next month.
For most players doing their own setups in the US, this is the practical choice. Good materials, no waiting, and the fine slots come out right.
Hosco Files: The Same Slot for Less
Hosco files come out of Japan, and here is the thing nobody tells you. They are widely held to be the same files StewMac sells, or close enough that you cannot tell the cut apart, for around half the price. Some players will argue this to the grave. Most of them have used both and shrugged.
I expected the cheaper file to be the compromise. The budget version you settle for and quietly regret. That is not what I found. Slot after slot, for the common gauges, the Hosco cut the same slot the StewMac did. The StewMac pulled ahead only on the very narrowest files and the finest finish work, where the grind is a hair more precise. Everywhere else the two were a wash. The price gap buys you US availability and the last few percent on a plain high E. It does not buy you a better slot on the strings that make up most of the set.
The catch is getting them. In the US you order them and you wait. If you can plan ahead, the value is real.
How to Pick the File for Each String
Match the file to the string. Not the string to the file.
For a plain string, pick a file one or two sizes over the string gauge. A plain string needs room to slide and it does not grip the slot walls the way a wound string does. A slot a couple thousandths wide of the string is right.
For a wound string, pick a file close to the string gauge. The winding is rough. It grips a loose slot and rattles, and it binds in a tight one. Close to the gauge, rounded bottom, and it sits quiet.
If you only buy a few files, buy the gauges you actually string with. A set of six covers a standard set with the plain strings sized up a touch. You do not need every gauge made. You need the ones under your strings.
Cutting It Without Ruining It
Go slow. The one mistake you cannot undo is a slot cut too deep.
Cut at the back angle from the start. Tip the file down toward the tuners so the slot slopes away from the front edge. Cut a few passes, then fret the string at the third fret and look at the gap over the first fret. You want a sliver of daylight, just enough that the open string clears the first fret without buzzing. Stop while the daylight is still there. A slot a hair too high plays fine and files down easy. A slot too low buzzes, and the only fix is a new nut.
When the height is right, run the string in the slot a few times to seat it. Pull it to pitch. Bend it. If it pings or lands sharp, the slot is too tight or the angle is wrong. Widen it a hair with the correct file, check the angle, and try again. A dab of pencil graphite in the slot helps the string slide, but if you need graphite to stop a ping, the slot is cut too tight. Fix the slot.
So Which File
If you need files this week, or you do most of your fine work on plain strings, buy the StewMac set. It is the US standard, it is on the bench in two days, and the narrow slots come out right. This is the choice for most players, and it is enough.
If you can plan ahead and the budget matters, the Hosco files cut the same slot on the common gauges for about half the money. Order early, wait on the shipping, and you have saved real cash for no loss where it counts.
Either way, the file is what makes the bone-versus-Tusq question matter or not. A good slot in a Tusq nut beats a bad slot in bone every day of the week. For the material side of the decision, our guide to bone, Tusq, and Corian nut materials covers what each one actually changes, and the brass and graphite comparison covers the two that get left out. Read those after you can cut a clean slot. Not before.
