Replacing Nuts on Acoustic Guitars
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Common Guitar Nut Material

Bone / Ivory nuts Bone nuts are dense, durable and many are fond of the tone. All bone and ivory nuts are carved from scratch to fit the instrument in hand. If dealing with an instruments for which there are no "ready made" replacement nuts, custom, hand carved nuts can be made to replace the original.

Ivory Nut I carved for a Martin

Tusq® nuts Tusq® is the brand name of a man made material quickly gaining in popularity. Tusq® nuts and saddles are used by Taylor, Gibson, Tacoma and many other manufacturers. These would be my recommendation for those seeking a ready made replacement nut.

I have most popular sizes of Tusq® nuts on hand for shop replacements. If you are looking to purchase just the nut you can check out Graph Tech's website. All ready made nuts must still be adjusted for string height and action after installation, most require some fitting to the neck.

Graph Tech Trem-Nuts® - Graphite nuts are popular on electric guitars with tremolo's. The use of a tremolo causes the string to be pulled back and forth thru the nut. To prevent string binding and possible breakage it is important that the string glide nicely thru the nut slots without sticking. View some available Trem-Nuts

Plastic Nuts - A great deal of instruments still come standard with plastic nuts. While these are O.K. it should be said that there is a vast difference amongst plastics. Cheaply made hollow, soft or spongy plastic nuts are sure to be a sustain and tone killa!

Nut is Hollow Thru it's center

Corian®  nuts- It's not just for your kitchen ya know... Corian is another synthetic material that has been used for nuts. It has a very bright white appearance and is used on nearly all Martin® instruments. If you really want to be different you could also consider using scrap Corian from your local home improvement store and create one in any number of colors.

Brass or Aluminum nuts These are not as common as other materials but some players gotta have 'em.  

  
Brass Nut laminated with plastic

Ebony / Wood Nuts Ebony has also been used by various manufacturers though it is most often seen on earlier instruments or less expensive models.

Locking & Specialty Electric Guitar Nuts

Locking Nuts - These are manufactured nuts found on electric guitars which "lock" the string at the nut to prevent string slippage and binding at the nut. Locking nuts are usually reserved for instruments with tremolos where strings are pulled frequently due to tremolo use.

Roller Nut - Used on electric guitars with tremolos, ball bearings ease the movement of the string across the nut.

Custom Made Nuts

Making a nut from scratch  Many inquire as to whether I can and will carve a nut for them without the instrument in hand and the answer is no. I do not offer to make nuts without installing them for many reasons, the primary one being common sense... there is a vast difference between carving a nut while fitting it to the instrument and merely trying to replicate an example. Also, when carving a new nut or installing a ready made, pre-slotted one some adjustments can only be made once the nut is in place. The final string slot depth which determines the height of the strings from the frets is cut after the nut has been installed and the instrument has been set up properly. The cuts made in the nuts string slots are done so with specialty files known to most as "nut files".  The price of a set of nut files normally runs about $75 and deters most do-it-yourselfers from making the attempt if it's a one time deal.
Lowering the action at the nut is normally quite inexpensive and usually a very simple matter.

Properly Adjusting the Nut

It is important to have the instrument set up properly before cutting the string slot depth in the nut. Cutting a slot too deeply will place the string against the first fret and result in buzzing.

Slot Depth The depth of the slots in the nut determine how closely the string comes to the frets, particularly the first fret. It is critical that the string have ample room to vibrate without contacting the first fret or you'll have an annoying open string buzz. Adversely, nut slots that have not been adjusted often leave the strings higher than necessary which creates discomfort and higher action. A minor adjustment (say .020) can make a very noticeable difference.

Slot Width Each string slot should just slightly exceed the diameter of it's string. If the slot is smaller than the string it may bind and create tuning problems. (And that annoying pinging sound when tuning up.)
If you've ever had to lift a string from the nuts slot when changing the strings...it's a sure sign the slot is too small.
An increase in string gauge equals an increase in string diameter and will sometimes require an adjustment to the slots width.
 
Slot Angle The slots must also be angled correctly. If the angle is too steep the string may actually rest on just a small portion of the slot causing premature wear as it is sitting on a small peak.
On instruments with minimal peghead angle the angle is especially critical for a clear clean sound. A poorly angled nut slot can create a jangly, buzz sound that can often be silenced if downward pressure is applied to the string behind the nut (over the peghead). This is often a sign that the string is not contacting the nut slot properly. The sound very closely mimics the sound of the string hitting the first fret when the slot is too deep.

Nut Height/Final Shape  Once the slots have been deepened I may remove material from the top of the nut, if need be, to avoid having the strings deeply "buried" in the nut. I want the slots deep enough to keep the strings from popping out when plucked but not so deep that they're buried. It looks clean and sharp as well.
 

Raising Action at the Nut

There are good reason's to salvage an original nut if possible. First of all vintage instruments often have lovely ivory and ebony nuts that are just too nice to scrap.
And of course, it is cheaper, especially if you have an instrument for which no pre-made plastic nut is available. When inexpensive instruments require the action raised at the nut and there are no similar pre-made nuts available we are left to choose between carving one by hand or raising the original.

My method of raising the nut is to laminate matching material to the bottom of the nut. I use the term "laminate" and not shim for a very good reason. Many place shims beneath a nut that will be destroyed if the nut is ever removed again. Wood shims are simply awful looking and it is quite common to find paper and cardboard placed there as well. When laminating material to the base of the nut it becomes permanent and very difficult to see. The nut can then be removed just as any other without replacing paper or wood shims that are easily destroyed when a nut must be removed.

I may use plastic, ivory or ebony as a laminate depending on the nut and it's coloring. While you may have read of a common practice of filling the slots with a mixture of superglue and bone dust I personally don't prefer that option. The "filler" that's glued to the bottom of the nut slot to raise it may eventually pop loose and on most instruments I can hear a noticeable change in sound, no question there.
Instead of filling the slots to raise their depth, I raise the nut as a whole which enables me to recut each string slot for proper width and angle.