Tusq XL nuts are impregnated with Teflon which reduces string binding and drag.
Tusq XL was formerly called Trem-nut.
Nut Width/Length
Nut width is measured from the outer edges of the nut itself. Slight adjustments are normally necessary to insure a new nut fits flush against the sides of the neck.
E to E Spacing
The space between the bass E string slot and the treble E string slot will indicate how closely the strings will lay to the edge of the fingerboard.
Too close and the string may fall off of the edge of the fingerboard.
Too far and finger space may feel crowded when making chords.
While there is a small margin of adjustment, the E to E spacing must be correct to insure the strings have a proper distance from the edge of the fingerboard.
Material
Popular nut material include bone, ivory, plastic, brass, corian and other materials.
The material a nut is made from will effect the tone.
Installing A New Nut
Some nuts are easy to tap loose and remove. Others have been installed before the instrument was sprayed and require delicate removal to avoid finish chips.