Fretbar Understring Leveler 18in - Precise Full Neck Fret Leveling

In this review the StewMac Fretbar Understring Leveler proves to be a practical specialty tool for luthiers, techs, and serious DIYers who want to level frets accurately without removing the strings. The biggest reason to buy is its ability to cover a wide span of frets while working under full string tension, which simplifies setups and preserves neck relief. Built from extruded aluminum and designed to use Stikit abrasives, this tool focuses on precision and repeatable results rather than gimmicks.

Key Features

• Original understring concept: Lets technicians level frets under full string tension, reducing setup steps and keeping string spacing consistent while working.
• 18in length for full neck coverage: The 18in fretbar spans most frets at once so users can establish an even plane without contacting the nut or saddle.
• Works with strings on or off: Offers flexibility to perform understring leveling or traditional leveling with strings removed depending on the job.
• Premium aluminum precision: Constructed from 6061 extruded aluminum with very tight tolerance for a flat, durable leveling reference.
• Compatible with Stikit abrasives: Designed to accept 1in wide 3M Stikit Gold abrasive for fast, clean material removal and consistent results.
• Lifetime Promise and support: Backed by the maker's lifetime support so buyers can get technical help and rely on long term durability.

Who It's For

The Fretbar Understring Leveler is best for professional guitar techs, luthiers, and advanced hobbyists who perform frequent fret leveling and want the option to work with strings in place. It excels when users need to preserve neck setup while achieving a single, consistent plane across multiple frets.

Less experienced hobbyists who have never used abrasive beams or understring techniques may prefer a simpler, shorter leveling beam or to seek instruction before attempting full neck work. This tool is specialized; it is not a complete fret dressing kit by itself.

Pros & Cons

Pros

• High build quality and durable 6061 aluminum construction for a reliable flat reference.
• Large 18in span speeds jobs by covering most frets at once and avoiding nut or saddle contact.
• Works with strings on or off, adding practical versatility for different workflow preferences.
• Designed to pair with Stikit abrasives for predictable, clean material removal.

Cons

• Specialized tool that presumes knowledge of fret leveling technique and compatible abrasives.
• Length and rigid profile may be more than needed for small instruments or very short necks.

Specifications

Brand	StewMac
Model type	Understring fretbar
Length	18in (457mm)
Width	0.75in (19mm)
Height	1.46in (37mm)
Material	6061 extruded aluminum
Abrasive compatibility	1in Stikit 3M Gold abrasives

Our Verdict

The StewMac Fretbar Understring Leveler is a focused, high quality tool for users who need accurate, repeatable fret leveling across most of a neck and want to work with strings in place. Its precision aluminum construction, compatibility with Stikit abrasives, and full neck span make it good value for pros and experienced hobbyists who already understand fret leveling technique.

Frequently Asked Questions

Can this be used with strings left on?
Yes, the tool is explicitly designed to work under the strings so you can level frets under full string tension.

What abrasives work best with the bar?
StewMac designed the bar to use 1in wide 3M Stikit Gold abrasives for clean, predictable material removal.

Is the length suitable for most guitars?
At 18in the bar covers most guitar necks and allows full span leveling without contacting the nut or saddle on standard instruments.