Tune-o-matic

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 Super 400 guitar in 1953 and the Les Paul Custom the following year. 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.

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 pitch 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 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.

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