How to Install a Neck Shim to Adjust Neck Angle

What a neck shim does

The neck angle is the tilt at which the neck meets the body. On bolt-on guitars, this angle is set by the depth and shape of the neck pocket. If the angle is off, the strings may sit too high or too low, and the bridge saddles may run out of adjustment range. A neck shim is a thin wedge placed under the heel of the neck to alter that angle.

Bolt-on necks appear on many electric guitars and acoustic-electric guitars. The heel fits into a pocket in the body and is secured with screws. Because the pocket is machined to a specific depth, variations in wood moisture or manufacturing tolerances can leave the angle slightly wrong. A shim is a non-invasive correction that does not require reshaping the pocket or the heel.

A properly installed shim can bring the bridge saddles back into their working range, improve string height consistency, and make intonation easier to set. It is a common repair that any player can do with basic tools.

• Corrects string height that is too low or too high across the fretboard
• Brings bridge saddles into a range where they still have adjustment room
• Reduces buzzing caused by a steep neck angle
• Improves playability without permanent modifications

When to use a neck shim

Before adding a shim, check the truss rod and bridge. If the neck has proper relief and the bridge saddles are already within their normal range, but the strings still feel wrong, the neck angle is the likely issue. A common sign is that the saddles are either bottomed out against the body or raised to their maximum height, and intonation is still inaccurate.

You might also notice that the guitar plays well in the middle of the neck but becomes difficult higher up. This often indicates the neck is angled too shallow, causing the strings to rise as they approach the body. Conversely, if the strings are so low that they fret out when you bend, the angle may be too steep. A shim can tilt the neck so string height increases or decreases evenly along the fretboard.

Never use a shim to mask a twisted neck, a warped body, or a badly worn fret. If the neck is straight and the pocket is clean, but the angle is still off, a shim is the right tool. For a complete understanding, review guitar action and setup and guitar neck joint styles before proceeding.

Choosing the right shim

Shims come in two main types: full-pocket and partial. A full-pocket shim covers the entire base of the neck pocket, giving an even tilt across the whole joint. A partial shim, often a small strip placed at the heel end, changes the angle more locally and works well for fine adjustments. The material matters as well: wood, plastic, and metal each have different compression characteristics.

Wood shims, often made of birch or maple, are traditional and can be sanded to a custom thickness. They tend to compress very slowly, but that means the setup may settle over time. Plastic and metal shims are more dimensionally stable and come in precise thicknesses, making them easier to reproduce in a production setting.

Many players use a business card as a temporary shim to test the effect, then replace it with a proper wood or plastic shim for a permanent repair. A shim that is too thick will tilt the neck too much, so start with the thinnest option that corrects the problem. Place partial shims at the back of the pocket, farthest from the fretboard, to get the most leverage.

Tools and preparation

You will need a Phillips-head screwdriver that fits the neck screws exactly, a soft cloth to protect the guitar's finish, and your chosen shim. A straightedge and a string action ruler are helpful for verifying the results. You may also want a set of feeler gauges to measure the gap under the neck heel, though this is not essential.

Place the guitar on a padded work surface. Loosen the strings enough to remove tension, but keep them on to hold the bridge and tuners in place. If you need to remove the neck completely, you can detach the strings at the tuners. Refer to how to remove a bolt-on guitar neck for detailed steps.

If you cut your own shim from wood or plastic, wear eye protection and work in a well-ventilated area. Loud sawing and sanding can exceed safe levels; sounds at or above 85 dBA can cause hearing loss over time (NIDCD, 2026). Use hearing protection and keep the work area free of debris.

Step-by-step installation

Start by placing the guitar on a clean, padded work surface. Partially loosen the strings until they are slack, but leave them attached to keep the nut and bridge seated. Remove the four neck screws and carefully lift the neck out of the pocket. Set the neck aside with the strings still attached, or remove the strings entirely if you prefer.

Inspect the neck pocket for debris, finish residue, or burrs. Sand any rough areas with fine-grit sandpaper if necessary. Decide whether you need a full-pocket or partial shim. For a full-pocket shim, cut it to match the shape of the pocket. For a partial shim, cut a small piece that covers the back of the pocket only (the end closest to the bridge). Position the shim in the pocket as intended.

Reattach the neck by aligning the screw holes and gently pushing the neck into place. Insert the screws and tighten them evenly, but do not fully torque them yet. With the strings still slack, use a straightedge to check the neck alignment and the angle relative to the body. Then bring the strings up to pitch gradually, checking the string height and the position of the bridge saddles. If the saddle is still not in a good range, adjust the shim thickness or reposition it.

Once you achieve a comfortable setup, tighten the neck screws to a firm, even pressure. Avoid overtightening, as this can strip the threads in the body. A common practice is to turn each screw until it is snug, then add a quarter turn. After the screws are tight, play a few chords and bends to confirm the feel.

After installation: adjust the setup

Inserting a shim changes the effective relief in the neck, so you will need to reset the truss rod. Aim for a slight bow, just enough to avoid buzzing, and check the gap at the 7th fret when the string is pressed at the first and last frets. Our truss rod adjustment guide explains the process in detail.

Next, set the string height at the bridge using the saddle height screws. The shim should have brought the saddles back into a usable range, allowing you to dial in the action cleanly. Finally, check intonation by playing the 12th fret harmonic and the fretted note; adjust the saddle position until they match. See guitar intonation for a full walkthrough.

Give the guitar a few days to settle. Wood may compress slightly under the shim, and you might need to re-tighten the neck screws or add a slightly thicker shim. This is normal. A well-fitted shim creates a stable contact that holds its setting for a long time.

What to pick for your setup

Questions

Can I use a business card as a shim?

A business card works as a temporary test, but it will compress over time and is not a lasting fix. For a permanent solution, use a proper wood or plastic shim that will hold its shape.

Should I tilt the neck forward or backward?

The direction depends on the problem. If the strings are too high, you need to tilt the neck backward (raise the heel) to lower them. If they are too low, place a very thin shim at the front of the pocket to tilt it forward. Always test with strings at full tension.

Can I install a shim on a set-neck guitar?

No. A shim works only with bolt-on necks because it sits in the neck pocket. Set-neck and neck-through guitars have the angle built into the joint, so adjusting them requires different methods, often a professional repair.

Will a shim affect the tone?

A shim changes the contact between the neck and body, which can subtly alter resonance. Using a wood shim that matches the pocket closely helps preserve the original sound. Most players find the effect negligible compared to the playability improvements.

How do I know if I need a shim rather than a truss rod adjustment?

If the neck is straight and the truss rod is set correctly, but the string height is still too high or too low across the fretboard, a shim is likely needed. If the problem is concentrated in the middle frets, adjust the truss rod first.