Anatomy of an Acoustic Guitar

The headstock

The headstock is the flat end of the neck. It holds the tuners (also called machine heads or tuning pegs): six geared posts that tighten or loosen each string. Most steel-string acoustics have three tuners on each side; some brands put all six on one side.

The headstock is usually angled back from the neck. That angle presses the strings down onto the nut, which keeps them from buzzing in their slots. On many guitars you will also find a small plastic cover just behind the nut: that is where the truss rod is adjusted.

The nut

The nut is a small strip with six slots, at the point where the headstock meets the fretboard. It sets the spacing of the strings at that end and the height of the strings above the first fret. Common materials are bone, plastic (often sold under names like Tusq or Micarta) and, on a few guitars, brass.

The nut matters more than its size suggests. Slots cut too high make the first few frets hard to press and pull the notes sharp. Slots cut too low make open strings buzz.

The neck and fretboard

The neck is the long piece you hold. Its back shape (often described as C, V or D) and its width at the nut decide how it feels in your hand. Steel-string acoustics are commonly 1 11/16 in (about 43 mm) or 1 3/4 in (about 44.5 mm) at the nut; classical guitars are wider, around 52 mm.

The fretboard (or fingerboard) is the strip glued to the front of the neck. Rosewood, ebony and composite boards are all common.

The frets are the metal bars across the fretboard. Pressing a string just behind a fret shortens the vibrating part of the string, and each fret raises the note by one semitone. Twelve frets up, the string plays the same note an octave higher, which is why the 12th fret sits exactly halfway between the nut and the saddle and usually has a double marker.

Position markers (dots or inlays) sit at frets 3, 5, 7, 9, 12, 15 and 17 on most guitars, with small matching dots on the side of the neck so you can see them while playing.

Inside the neck runs the truss rod, a steel rod that counteracts the pull of the strings. Steel strings at standard tension pull hard on the neck, and the rod sets how much the neck bows forward (called relief). Many classical guitars have no truss rod because nylon strings pull far less.

Where the neck meets the body

The heel is the thick block at the back of the neck where it joins the body. Most modern steel-string guitars join the body at the 14th fret; classical guitars and some vintage-style steel-strings join at the 12th. A 14-fret neck gives easier reach to the higher frets. A cutaway is a scoop taken out of the upper body next to the neck so you can reach even higher.

The body

The body is a hollow box made of three parts.

• Top (soundboard). The thin front plate, usually spruce or cedar, sometimes mahogany or koa. It does most of the work of making sound. A solid top is made of solid wood, usually two book-matched halves glued at the centre seam; a laminate top is several thin layers glued together. Solid tops vibrate more freely; laminates are tougher and less sensitive to humidity.
• Back and sides. These reflect and colour the sound. Mahogany, rosewood, maple and laminates are common. The sides are bent to shape and joined to the top and back with thin strips called linings.
• Binding. The strip along the edges of the top and back. It seals the end grain and protects the edges from knocks.

The outline has three named areas: the upper bout (the narrower part near the neck), the waist (the narrow middle) and the lower bout (the widest part, where the bridge sits). Body styles such as dreadnought, OM and jumbo are mostly defined by these widths and the body depth.

Bracing: the part you cannot see

Thin wooden braces are glued under the top and across the back. They stop the top from folding under string tension while still letting it vibrate. Steel-string guitars almost always use an X-brace pattern, where two main braces cross just below the soundhole. Classical guitars usually use fan bracing, a set of thin braces spread out like a fan below the soundhole. Bracing is a big reason two guitars with the same woods can sound different.

The soundhole and rosette

The soundhole lets air move in and out of the body, and that air movement is a large part of the low end you hear. The decorative ring around it is the rosette. It also reinforces the top around the hole. Through the soundhole you can usually see the maker’s label and, on electric-acoustics, the pickup or preamp.

The pickguard is the thin plastic plate next to the soundhole. It protects the top from pick scratches. Classical guitars rarely have one, because they are played with the fingers.

The bridge, saddle and pins

The bridge is the wooden piece glued to the top in the lower bout. It anchors the strings and passes their vibration into the top.

The saddle is the thin strip set into a slot in the bridge. Along with the nut, it is one of the two points the strings rest on, and its height sets how high the strings sit above the frets (the action). Its exact position, slightly angled on most steel-string guitars, is what keeps each string in tune as you play up the neck. On many electric-acoustics a thin pickup lies under the saddle.

Bridge pins hold the ball end of each steel string in the bridge. Classical guitars have no pins: the nylon strings are tied around the bridge instead.

Scale length is the vibrating length of the open string, from nut to saddle. Common steel-string scales are about 24.75 in (Gibson-style) and 25.4 in (Martin-style); a classical guitar is usually 650 mm. A longer scale puts the strings under more tension at the same pitch, which feels a little stiffer.

The strings

A standard guitar has six strings, numbered from the thinnest:

Steel strings are wound with bronze or phosphor bronze (materials and gauges compared in acoustic guitar strings). Classical guitars use nylon trebles and nylon basses wrapped in silver-plated copper. Never put steel strings on a guitar built for nylon: the extra tension can damage the neck and pull the bridge off. To tune all six, use the guitar tuner.

The end pin and strap button

At the very bottom of the body is the end pin or strap button. On an electric-acoustic it is often combined with the output jack, so you plug the cable in at the same spot where the strap attaches. A second strap button, if there is one, is usually on the heel.

Parts that wear and need care

Most parts last the life of the guitar, but a few need regular attention:

• Strings go dull and won’t stay in tune after weeks to months of playing. See how much it costs to restring an acoustic guitar.
• Frets wear grooves under the strings you play most, which leads to buzzing.
• The saddle and nut can be swapped or adjusted to change the action.
• The neck relief and the top move with humidity and season. Our guide to whether your guitar needs a setup covers the signs.