Tune-o-matic (also abbreviated to TOM) is a name of fixed bridge design for electric guitars. It was designed by Ted McCarty (Gibson Guitar Corporation president) and introduced in the Gibson Les Paul Custom guitar in 1954.[1] In 1955, it was used on the Gibson Les Paul Gold Top. It was gradually accepted as a standard on almost all Gibson fixed-bridge guitars, replacing the previous wrap-around bridge design, except on the budget series.[2]
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Guitar strings, especially steel strings, are not ideal vibrators. Generally the thicker the string, the shorter the effective length. This refers to the length of string involved in producing a sound, as opposed to the length between the nut and the bridge. Many guitar designs with fixed bridges have the bridge slanted or stepped so that the distance from nut to bridge is larger for thick strings. The Tune-o-matic extends this idea to make the distance adjustable for all the strings, within limits.
A common way of determining correct adjustment for a string is to compare the note at the 12th fret with the harmonic at the same position. The two should be as close as possible.
The Tune-o-matic bridge consists of two adjustable posts that are screwed into the guitar body and a bar between these posts. The bar has six saddles, one per string. Each saddle has a small groove that matches string gauge and shape — it is where the string would be held by the saddle. When fully assembled, each string sits astride a saddle and the saddle thus "marks" the end of the vibrating string. Each saddle can be adjusted (moved back and forward) with a screw to control intonation. To prevent saddles from falling out of the bridge when no strings are installed, most models hold the saddles with a retainer wire or wires.
After the passing over the saddles each string goes to the tailpiece. Some guitars have a stopbar to hold strings, others have "strings through the body" construction which uses the body of the guitar to hold the end of the strings.
The Tune-o-matic bridge is not absolutely flat; and standard Gibson Tune-o-matic bridges have a 12" radius.[1] Ideally, the radius should match the radius of fretboard for the most comfortable playing experience.
It is possible to fit the bridge either way round on the two body posts, which leads to a certain amount of confusion when changing strings, should the bridge fall off. Conventionally, the string length (intonation) adjustment screw heads of the older "Vintage" bridge face the neck, and the screw heads of the newer "Nashville" bridge face the stopbar. Unless the player wishes to completely reset the action and intonation, it is important to refit the bridge in the same orientation as before a string change, regardless of which way round it was to start with.
Since its invention, different versions by Gibson and other companies have emerged. Gibson has introduced at least three versions that have minor differences in construction[2]:
There are multiple widely known Tune-o-matic models that differ in the following parameters:[3]
| Model | 1st-to-6th distance, mm | Between posts, mm | Post, diameter × length, mm | Thumbwheel diameter, mm | Saddles, mm | |||
|---|---|---|---|---|---|---|---|---|
| width | height | thickness | hole | |||||
| Gibson BR-010, ABR-1 ("Vintage") | 52 | 73.8 | M4×30 | 15 | 8.8 | 6.5 | 3.0 | M3 |
| Gotoh GE-103B, GEP-103B[4] | 52 | 74 | M4×30 | 16 | 8.8[3] | 8.0[3] | 3.0[3] | M2.5[3] |
| Gotoh GE-103B-T, GEP-103B-T[4] | 52 | 74 | M8×33.5 | 15 | 8.8[3] | 8.0[3] | 3.0[3] | M2.5[3] |
| Gibson BR-030 ("Nashville") | 51.6 | 74.3 | M5×25.1 | 16 | 8.8 | 10.8 | 2.55 | M3 |
Over time, particularly on the thinner unwound E, B and G strings - the groove cut into the saddle, in which the string rests, takes on a sharper 'V' shape - due to the action of the string sliding slightly in the groove: particularly during string bending. As this 'V' shape sharpens, it takes on a slight scissor characteristic and gradually any new string is abraded as string tension pulls it deeper into the groove: this leads to increased breakage, particularly during bending - exactly at the saddle. The simplest solution is a slight filing out of the groove, to recreate more of a 'U' shape, while saddle replacement - particularly with very high quality metal alloy replacements, is another option.
There is no general consensus on "proper" capitalization of bridge name. Gibson's official site usually spells it as "Tune-o-matic",[1] while "Tune-o-Matic" and "Tune-O-Matic" are frequently used in advertising and promotional material.