StewMac Understring Radius Gauge Tool Set of 9 - Extra-Wide Bass Setup

In this review the StewMac Understring Radius Gauge set is evaluated as a practical toolkit for bass players and techs who need accurate saddle and pickup alignment. The single biggest reason to buy is its combination of an easy-to-read low profile and a matched top-and-bottom curvature that lets a user measure fretboard radius with strings on and then transfer that curve to bridge saddles for faster, repeatable setups. The review focuses on how the set fits bass work and why the extra-wide span matters for wider string spreads.

Key Features

• Set of 9 radii: Includes 7-1/4in, 9-1/2in, 10in, 12in, 14in, 15in, 16in, 17in and 20in to match vintage and modern fretboard arcs.
• Understring low profile: Slim shape lets you read fretboard radius with the strings on, so measurements can be done without removing strings.
• Top and bottom matching arcs: Bottom curvature determines the fretboard radius and the matching top curvature becomes a direct reference for setting saddle heights.
• Extra-wide span: Covers string spreads up to 3-3/4in (95.25mm), making it suitable for most 4-string and 5-string basses and many 6-string basses.
• Durable steel construction: Steel gauges hold their radiused shape for repeated use in workshop and stage environments.

Who It's For

The set is aimed at bass players, luthiers and techs who perform routine setups and want a simple, reliable way to match saddle heights to the fretboard arc without complex jigs. It is particularly useful for shops that service 4-string and 5-string basses and for players who prefer to check radius with the strings installed.

Players who only need a single radius or who prefer digital profiling tools may not need the full nine-piece set. Also, those working exclusively on narrow-spread electric guitars with string spreads under the stated span could use a smaller or different gauge solution.

Pros & Cons

Pros

• Fast and accurate transfer of fretboard radius to bridge saddles for improved playability.
• Low profile design allows radius reading with strings on, saving time and avoiding restringing.
• Extra-wide width accommodates wide string spreads common on basses and some extended-range guitars.
• Steel construction is robust and resists wear from repeated use.

Cons

• The full nine-piece set may be more than needed for someone who only uses one or two radii.
• The gauges are physical tools only and do not replace digital measuring for complex profiling work.

Specifications

Brand	StewMac
Number of gauges	9 pieces
Included radii	7-1/4in, 9-1/2in, 10in, 12in, 14in, 15in, 16in, 17in, 20in
Maximum string spread	3-3/4in (95.25mm)
Material	Durable steel

Our Verdict

The StewMac Understring Radius Gauge set is a practical, high-value tool for bass setup work where fast, repeatable saddle height matching matters. It is especially worthwhile for techs and players who service a variety of bass radii and want the convenience of measuring with strings on; those with minimal radius needs or who prefer digital profiling may not need the full set.

Frequently Asked Questions

Can these gauges be used with strings on?
Yes, the low profile and slim shape are specifically designed to let you read the fretboard radius with the strings installed.

Will the set fit 5-string and 6-string basses?
The extra-wide gauges span up to 3-3/4in (95.25mm), making them ideal for 4-string and 5-string basses and suitable for many 6-string basses.

What is the construction material?
The gauges are made of durable steel so they maintain their radiused arcs through repeated use.