Understring Radius Gauges Set of 9 - Precise Guitar Setup Tools

In this review the StewMac Understring Radius Gauges set is judged as a practical, pro-level tool kit for anyone who does regular guitar or bass setup work. The bottom line: this set of nine slim-profile gauges makes matching saddle and pickup heights to fretboard curvature straightforward and accurate, so the biggest reason to buy is predictable, repeatable setup results without removing strings. It suits techs and serious hobbyists who value reliable measurements from a tool backed by a lifetime promise.

Key Features

• Complete range: The set includes 7-1/4in through 20in radii so a single kit covers common acoustic, electric and bass fretboard arcs.
• Standard width: Each gauge fits string spreads up to 2-5/8in, which is ideal for most 6-string guitars and typical 4-string basses.
• Dual-surface accuracy: Matching top and bottom arcs let you read the fretboard radius on the bottom and set saddle or polepiece heights on the top for consistent curvature alignment.
• Low profile for on-string use: The slim design slides under strings so you can measure and adjust without detaching strings, saving time and preserving setup alignment.
• Durable construction: Built for long service and backed by a lifetime promise, these gauges are meant to be a workshop staple.

Who It's For

The set is aimed at professional luthiers, repair shop technicians and dedicated home builders who need precise, repeatable tools for setup tasks. Anyone who frequently adjusts saddles, bridges or pickup polepieces will benefit from the ability to match string height to the board arc quickly.

Less technical owners who only perform occasional basic adjustments might find a single-radius tool or a cheaper single-piece gauge adequate; this full nine-piece set is most cost-effective for people who work on multiple instrument types or require the full range of radii.

Pros & Cons

Pros

• Well-made and accurate, letting techs perform precise saddle and polepiece alignment.
• Low-profile design allows measurements and adjustments without removing strings, speeding setup work.
• The nine-radius range covers common guitar and bass radii so one kit handles most instruments.
• Backed by a lifetime promise for long-term durability and support.

Cons

• The standard-width set fits string spreads up to 2-5/8in, so it may not suit extended-range or wide-spread instruments.

Specifications

Our Verdict

The StewMac Understring Radius Gauges set is a smart buy for anyone who performs regular setups on 6-string guitars and most 4-string basses. It delivers accurate, repeatable measurements thanks to matching top and bottom arcs and a slim profile that works under strings, making it good value for workshops and serious hobbyists who need reliable results.

Frequently Asked Questions

Can I use these gauges without removing strings?
Yes, the low-profile design lets you slide the gauges under strings to read fretboard radius and set saddles or polepieces without detaching strings.

Will the standard set fit my bass?
The standard width fits string spreads up to 2-5/8in, which covers most 4-string basses; wider-stringed basses may require an extra-wide gauge set.

Are these durable workshop tools?
Yes, they are built for long-term use and come with a lifetime promise and expert tech support for service questions.