StewMac Fretbar Understring Leveler 9in - Precision Fret Leveling Tool

In this review the StewMac Fretbar Understring Leveler proves to be a practical, purpose-built tool for luthiers and home techs who service short-scale instruments and need reliable fret leveling without removing strings. The single biggest reason to buy is its ability to work under full string tension, which saves time and preserves setup while delivering consistent results. For anyone who works on ukuleles, mandolins or who needs spot leveling on larger guitars, this tool consistently performs like a small, stiff beam you can trust.

Key Features

• Original understring design: Allows fret leveling with strings on, letting the technician check and correct high frets under real playing tension.
• 9in fretbar size: Sized for ukuleles, mandolins and short-scale necks while still usable for spot-leveling on full-scale guitars.
• Works with strings on or off: Gives the user flexibility to level frets under full string tension or perform traditional leveling with strings removed.
• Premium aluminum precision: Machined from 6061 extruded aluminum with tight straightness tolerances for accurate, repeatable passes.
• Compatible with Stikit abrasives: Accepts 1in Stikit abrasive strips for fast, clean material removal and easy maintenance of the leveling surface.
• Lifetime support: Backed by a lifetime promise and tech support to help troubleshoot technique and get consistent results.

Who It's For

The Fretbar is aimed at professional luthiers, techs and serious hobbyists who service ukuleles, mandolins, short-scale guitars and who appreciate the time savings of leveling under tension. It is particularly useful for setups where string tension affects fret height or where multiple quick, accurate spot passes are needed.

It is less useful for someone who never works on small instruments or who requires a full-length beam for complete guitar fretboard jobs. Those needing a full-length leveling bar for every string across a full-scale neck should consider complementary full-size tools.

Pros & Cons

Pros

• High build quality and a rigid feel that mirrors more expensive leveling beams.
• Effective understring operation saves time and preserves instrument setup during work.
• Works seamlessly with 1in Stikit abrasives for controlled, clean material removal.
• Small size and weight make it easy to position between strings on compact instruments.

Cons

• At 9in it is not a substitute for a full-length beam when you need to level an entire full-scale fretboard in one pass.
• Requires compatible 1in abrasive strips for best results, which may be an additional purchase.

Specifications

Product	Fretbar Understring Leveler
Length	9in (228mm)
Cross section	0.75in x 1.46in (19mm x 37mm)
Material	6061 extruded aluminum
Accuracy	0.0015in per ft guaranteed straightness
Abrasive compatibility	1in Stikit Gold abrasive strips
Use cases	Ukulele, mandolin, spot-level guitar fretwork

Our Verdict

The StewMac Fretbar Understring Leveler is a smart, well-made tool for anyone who works on short-scale instruments or needs accurate spot leveling on larger necks. Its ability to operate under string tension, solid aluminum construction and compatibility with Stikit abrasives make it a valuable addition to a luthier bench, offering good long-term value for focused fret work.

Frequently Asked Questions

Can it level frets with the strings on?
Yes. The understring design is intended to fit under and between strings so you can level frets under full string tension.

What instruments is the 9in size best for?
The 9in length is ideal for ukuleles, mandolins and other short-scale instruments, and it also works for spot leveling on full-scale guitars.

What abrasives does it use?
It is designed to work with 1in Stikit Gold abrasive strips for fast, clean fret leveling passes.