Headstock

The headstock is located at the end of the guitar neck furthest from the body. It is fitted with machine heads that adjust the tension of the strings, which in turn affects the pitch. Traditional tuner layout is "3+3" in which each side of the headstock has three tuners (such as on Gibson Les Pauls). In this layout, the headstocks are commonly symmetrical. Many guitars feature other layouts as well, including six-in-line (featured on Fender Stratocasters) tuners or even "4+2" (Ernie Ball Music Man). However, some guitars (such as Steinbergers) do not have headstocks at all, in which case the tuning machines are located elsewhere, either on the body or the bridge.

Nut

The nut is a small strip of bone, plastic, brass, corian, graphite, stainless steel, or other medium-hard material, at the joint where the headstock meets the fretboard. Its grooves guide the strings onto the fretboard, giving consistent lateral string placement. It is one of the endpoints of the strings' vibrating length. It must be accurately cut, or it can contribute to tuning problems due to string slippage, and/or string buzz.

Fretboard

Also called the fingerboard, the fretboard is a piece of wood embedded with metal frets that comprises the top of the neck. It is flat on classical guitars and slightly curved crosswise on acoustic and electric guitars. The curvature of the fretboard is measured by the fretboard radius, which is the radius of a hypothetical circle of which the fretboard's surface constitutes a segment. The smaller the fretboard radius, the more noticeably curved the fretboard is. Most modern guitars feature a 12" neck radius, while older guitars from the '60's and '70's usually feature a 6" - 8" neck radius. Pinching a string against the fretboard effectively shortens the vibrating length of the string, producing a higher pitch. Fretboards are most commonly made of rosewood, ebony, maple, and sometimes manufactured or composite materials such as HPL or resin. See below on section 'Neck" for the importance of the length of the fretboard in connection to other dimensions of the guitar.

Frets

Frets are metal strips (usually nickel alloy or stainless steel) embedded along the fretboard and located at exact points that divide the scale length in accordance with a specific mathematical formula. Pressing a string against a fret determines the strings' vibrating length and therefore its resultant pitch. The pitch of each consecutive fret is defined at a half-step interval on the chromatic scale. Frets worn down from heavy use can be replaced or, to a certain extent, re-shaped as required. Frets are available in different gauges.

Frets are laid out to a mathematical ratio that results in equal tempered division of the octave. The ratio of the spacing of two consecutive frets is the twelfth root of two , whose numeric value is about 1.059463. The twelfth fret divides the scale length in two exact halves and the 24th fret position divides the scale length in half yet again. Every twelve frets represents one octave. In practise, luthiers determine fret positions using the constant 17.817, which is derived from the twelfth root of two. The scale length divided by this value yields the distance from the nut to the first fret. That distance is subtracted from the scale length and the result is divided in two sections by the constant to yield the distance from the first fret to the second fret. Positions for the remainder of the frets are calculated in like manner.

There are several different fret gauges, which can be fitted according to player preference. Among these are "jumbo" frets, which have much thicker gauge, allowing for use of a slight vibrato technique from pushing the string down harder and softer. "Scalloped" fretboards, where the wood of the fretboard itself is "scooped out" between the frets allows a dramatic vibrato effect. Fine frets, much flatter, allow a very low string-action but require other conditions such as curvature of the neck to be well maintained in order to prevent buzz.

Truss rod

The truss rod is a metal rod that runs along the inside of the neck. It is used to correct changes to the neck's curvature caused by the neck timbers aging, changes in humidity or to compensate for changes in the tension of strings. The tension of the rod and neck assembly is adjusted by a hex nut or an allen-key bolt on the rod, usually located either at the headstock, sometimes under a cover, or just inside the body of the guitar underneath the fretboard and accessible through the sound hole. Some truss rods can only be accessed by removing the neck. The truss rod counteracts the immense amount of tension the strings place on the neck, bringing the neck back to a straighter position. Turning the truss rod clockwise will tighten it, counteracting the tension of the strings and straightening the neck or creating a backward bow. Turning the truss rod counter-clockwise will loosen it, allowing string tension to act on the neck and creating a forward bow. Adjusting the truss rod affects the intonation of a guitar as well as the height of the strings from the fingerboard, called the action. Some truss rod systems, called "double action" truss systems, tighten both ways, allowing the neck to be pushed both forward and backward (standard truss rods can only be released to a point beyond which the neck will no longer be compressed and pulled backward). Classical guitars do not require truss rods as their nylon strings exert a lower tensile force with lesser potential to cause structural problems.

Inlays

Inlays are visual elements set into the exterior surface of a guitar. The typical locations for inlay are on the fretboard, headstock, and on acoustic guitars around the soundhole, known as the rosette. Inlays range from simple plastic dots on the fretboard to intricate works of art covering the entire exterior surface of a guitar (front and back). Some guitar players have used LEDs in the fretboard to produce a unique lighting effects onstage.

Fretboard inlays are most commonly shaped like dots, diamond shapes, parallelograms, or large blocks in between the frets. Dots are usually inlaid into the upper edge of the fretboard in the same positions, small enough to be visible only to the player. Some older or high-end instruments have inlays made of mother of pearl, abalone, ivory, coloured wood or other exotic materials and designs. Simpler inlays are often made of plastic or painted. High-end classical guitars seldom have fretboard inlays as a well trained player is expected to know his or her way around the instrument.

In addition to fretboard inlay, the headstock and soundhole surround are also frequently inlaid. The manufacturer's logo or a small design is often inlaid into the headstock. Rosette designs vary from simple concentric circles to delicate fretwork mimicing the historic rosette of lutes. Bindings that edge the finger and sound boards are sometimes inlaid. Some instruments have a filler strip running down the length and behind the neck, used for strength and/or to fill the cavity through which the trussrod was installed in the neck.

Elaborate inlays are a decorative feature of many limited edition, high-end and custom-made guitars. Guitar manufacturers often release such guitars to celebrate significant or historic milestones.

Neck

A guitar's frets, fretboard, tuners, headstock, and truss rod, all attached to a long wooden extension, collectively constitute its neck. The wood used to make the fretboard will usually differ from the wood in the rest of the neck. The bending stress on the neck is considerable, particularly when heavier gauge strings are used , and the ability of the neck to resist bending is important to the guitar's ability to hold a constant pitch during tuning or when strings are fretted. The rigidity of the neck with respect to the body of the guitar is one determinant of a good instrument versus a poor one. The shape of the neck can also vary, from a gentle "C" curve to a more pronounced "V" curve. There are many different types of neck profiles available, giving the guitarist many options. Some aspects to consider in a guitar neck may be the overall width of the fingerboard, scale (distance between the frets), the neck wood, the type of neck construction (for example, the neck may be glued in or bolted on), and the shape (profile) of the back of the neck. Other type of material used to make guitar necks are graphite (Steinberger guitars), aluminium (Kramer Guitars, Travis Bean and Veleno guitars), or carbon fiber (Modulus Guitars and ThreeGuitars).

Neck joint or 'Heel'

This is the point at which the neck is either bolted or glued to the body of the guitar. Almost all acoustic guitars, with the primary exception of Taylors, have glued (otherwise known as set) necks, while electric guitars are constructed using both types.

Commonly used set neck joints include mortise and tenon joints (such as those used by CF Martin & Co. guitars), dovetail joints (also used by CF Martin on the D28 and similar models) and Spanish heel neck joints which are named after the shoe they resemble and commonly found in classical guitars. All three types offer stability. Bolt-on necks, though they are historically associated with cheaper instruments, do offer greater flexibility in the guitar's set-up, and allow easier access for neck joint maintenance and repairs.

Another type of neck, only available for solid body electric guitars, is the neck-through-body construction. These are designed so that everything from the machine heads down to the bridge are located on the same piece of wood. The sides (also known as wings) of the guitar are then glued to this central piece. Some luthiers prefer this method of construction as they claim it allows better sustain of each note. Some instruments may not have a neck joint at all, having the neck and sides built as one piece and the body built around it.

Strings

Modern guitar strings are manufactured in either metal or organo-carbon material. Instruments utilising "steel" strings may have strings made of alloys incorporating steel, nickel or phosphor bronze. Classical and flamenco instruments have historically used gut strings but these have been superceeded by nylon and carbon-fibre materials. Bass strings for both instruments are wound rather than monofilament.

Guitar strings are strung almost parallel to the neck, whose surface is covered by the fingerboard (fretboard). By depressing a string against the fingerboard, the effective length of the string can be changed, which in turn changes the frequency at which the string will vibrate when plucked. Guitarists typically use one hand to pluck the strings and the other to depress the strings against the fretboard.

The strings may be plucked using either the fingers or a variety of pick designs mostly associated with acoustic players.

Body (acoustic guitar)

In acoustic guitars, string vibration is transmitted through the bridge and saddle to the body via sound board. The sound board, typically made of tonewoods such as spruce or cedar. Timbers for tone woods are chosen for both strength and ability to tranfer mechanical energy from the strings to the air within the guitar body. Sound which is further shaped by the characteristics of the guitar body's resonant cavity.

In electric guitars, transducers known as pickups convert string vibration to an electric signal, which in turn is amplified and fed to speakers, which vibrate the air to produce the sound we hear. Nevertheless, the body of the electric guitar body still performs a role in shaping the resultant tonal signature.

The body of the acoustic instrument is thought to be a major determinant of the overall sound quality. The guitar top, or soundboard, is a finely crafted and engineered element made of tonewoods such as spruce and red cedar. This thin, often only 2 or 3mm thick, piece of wood, strengthened by differing types of internal bracing, is considered by many luthiers to be the dominant factor in determining the sound quality of a guitar. The majority of the instrument's sound is heard through the vibration of the guitar top as the energy of the vibrating strings is transferred to it.

Body size, shape and style has changed over time, 19th century guitars, now known as salon guitars, were smaller than modern instruments. Differing patterns of internal bracing have been used over time by luthiers, (Torres, Hauser, Ramirez, Fleta, and C.F. Martin being among the most influential designers of their time). Bracing not only strengthens the top against potential collapse due to the stress exerted by the tensioned strings, but also affects the resonance characteristics of the top. The back and sides are made out of a variety of timbers such as mahogany, Indian rosewood and highly regarded Brazilian rosewood (Dalbergia nigra). Each one is primarily chosen for their aesthetic effect and can be decorated with inlays and purfling.

The body of an acoustic guitar has a sound hole through which sound is projected. The sound hole is usually a round hole in the top of the guitar under the strings. Air inside the body vibrates as the guitar top and body is vibrated by the strings, and the response of the air cavity at different frequencies is characterised, like the rest of the guitar body, by a number of resonance modes at which it responds more strongly.

Instruments with larger areas for the guitar top were introduced by Martin in an attempt to create louder volume levels(although tone quality will also be affected by materials used in guitar top size and design). The popularity of the Dreadnought body size amongst acoustic performers is related to the greater sound volume produced.

Body (electric guitar)

Most electric guitar bodies are made of wood and include a plastic pick guard. Boards wide enough to use as a solid body are very expensive due to the worldwide depletion of hardwood stock since the 70's, so the wood is rarely one solid piece. Most bodies are made of two pieces of wood with some of them including a seam running down the centre line of the body. The most common woods used for electric guitar body construction include maple, basswood, ash, poplar, alder, and mahogany. Many bodies will consist of good sounding but inexpensive woods, like ash, with a "top", or thin layer of another, more attractive wood (such as maple with a natural "flame" pattern) glued to the top of the basic wood. Guitars constructed like this are often called "flame tops". The body is usually carved or routed to accept the other elements, such as the bridge, pickup, neck, and other electronic components. Most electrics have a polyurethane or nitrocellulose lacquer finish. Other alternative materials to wood, are used in guitar body construction. Some of these include carbon composites, plastic material (such as polycarbonate) and aluminium alloys.

Pickups

Pickups are transducers attached to a guitar that detect (or "pick up") string vibrations and convert the mechanical energy of the string into electrical energy. The resultant electrical signal can then be electronically amplified. The most common type of pickup is electromagnetic in design. These contain magnets that are tightly wrapped in a coil, or coils, of copper wire. Such pickups are usually placed right underneath the guitar strings. Electromagnetic pickups work on the same principles and in a similar manner to an electrical generator. The vibration of the strings causes a small voltage to be created in the coils surrounding the magnets, this signal voltage is later amplified.

Traditional electromagnetic pickups are either single-coil or double-coil. Single coil pickups are susceptable to noise induced from electric fields, usually mains-frequency (60 or 50 hertz) hum. The introduction of the double-coil humbucker in the mid 50's did away with this problem through the use of two coils, one of which is wired in a reverse polarity orientation.

The type and model of pickups used can greatly affect the tone of the guitar. Typically, humbuckers, which are two magnet/coil assemblies attached to each other are traditionally associated a heavier sound. Single coil pickups, one magnet wrapped in copper wire, are used by guitarists seeking a brighter, twangier sound with greater dynamic range.

Modern pickups are tailored to the sound desired. A commonly applied approximation used in selection of pickup is that less wire (lower dc resistance) = brighter sound, more wire = "fat" tone. Other options include specialized switching that produces coil-splitting, in/out of phase and other effects. Guitar circuits are either active, needing a battery to power their circuit, or, as in most cases, equipped with a passive circuit.

Fender Stratocaster type guitars generally utilize 3 single coil pickups, while most Gibson Les

Paul types use humbucker pickups.

Piezoelectric, or piezo, pickups represent another class of pickup. These employ piezoelectricity to generate the musical signal and are popular in hybrid electro-acoustic guitars. A crystal is located under each string, usually in the saddle. When the string vibrates, the shape of the crystal is distorted, and the stresses associated with this change produce tiny voltages across the crystal that can be amplified and manipulated.

Some piezo equipped guitars use what is known as a hexaphonic pickup. "Hex" is a prefix meaning six. In a hexaphonic pickup separate outputs are obtained from discrete piezoelectric pickups for each of the six strings. This arrangement allows the signal to be easily modified by on-board modelling electronics, as in the Line 6 Variax brand of electric guitars, the guitars allow for a variety of different sounds to be obtained by digitally manipulating the signal. This allows a guitar to mimic many vintage models of guitar, as well as output alternate tunings without the need to adjust the strings.

Another use for hexaphonic pickups is to send the output signals to a MIDI interpretation device, which determines the note pitch, duration, attack and decay characteristics and so forth. The MIDI (Musical Instrument Digital Interface) interpreter then sends the note information to a sound bank device. The resulting sound can closely mimic numerous types of instrument.

Electronics

On guitars that have them, these components and the wires that connect them allow the player to control some aspects of the sound like volume or tone. These at their simplest consist of passive components such as potentiometers and capacitors, but may also include specialized integrated circuits or other active components requiring batteries for power, for preamplification and signal processing, or even for assistance in tuning. In many cases the electronics have some sort of shielding to prevent pickup of external interference and noise.

Lining, Binding, Purfling

The top, back and ribs of an acoustic guitar body are very thin (1-2 mm), so a flexible piece of wood called lining is glued into the corners where the rib meets the top and back. This interior reinforcement provides 5 to 20 mm of solid gluing area for these corner joints. Solid linings are often used in classical guitars, while kerfed lining is most often found in steel string acoustics. Kerfed lining is also called kerfing (because it is scored, or kerfed to allow it to bend with the shape of the rib).

During final construction, a small section of the outside corners is carved or routed out and then filled with binding material on the outside corners and decorative strips of material next to the binding, which are called purfling. This binding serves to seal off the endgrain of the top and back. Purfling can also appear on the back of an acoustic guitar, marking the edge joints of the two or three sections of the back.

Binding and purfling materials are generally made of either wood or plastic.

Bridge

The main purpose of the bridge on an acoustic guitar is to transfer the vibration from the strings to the soundboard, which vibrates the air inside of the guitar, thereby amplifying the sound produced by the strings.

On both electric and acoustic guitars, the bridge holds the strings in place on the body. There are many varied bridge designs. There may be some mechanism for raising or lowering the bridge to adjust the distance between the strings and the fretboard (action), and/or fine-tuning the intonation of the instrument. Some are spring-loaded and feature a "whammy bar", a removable arm which allows the player to modulate the pitch moving the bridge up and down. The whammy bar is sometimes also referred to as a "tremolo bar" (see Tremolo for further discussion of this term - the effect of rapidly changing pitch produced by a whammy bar is more correctly called "vibrato"). Some bridges also allow for alternate tunings at the touch of a button.

On almost all modern electric guitars, the bridge is adjustable for each string so that intonation stays correct up and down the neck. If the open string is in tune but sharp or flat when frets are pressed, the bridge can be adjusted with a screwdriver or hex key to remedy the problem. In general, flat notes are corrected by moving the bridge forward and sharp notes by moving it backwards. On an instrument correctly adjusted for intonation, the actual length of each string from the nut to the bridge saddle will be slightly but measurably longer than the scale length of the instrument. This additional length is called compensation, which flattens all notes a bit to compensate for the sharping of all fretted notes caused by stretching the string during fretting.

Pickguard

Also known as a scratchplate. This is usually a piece of laminated plastic or other material that protects the finish of the top of the guitar from damage due to the use of a plectrum or fingernails. Electric guitars sometimes mount pickups and electronics on the pickguard. It is a common feature on steel-string acoustic guitars. Vigorous performance styles such as flamenco, which can involve the use the guitar as a percussion instrument, call for a scratchplate to be fitted to nylon-string instruments.