McGrath Guitars Bass String Spacing Gauge 4, 5, 6-String Basses 17mm to 19mm - SSG

The McGrath String Spacing Gauge

Cormac McGrath wanted a tool like this for a long time, so he sat down and made it himself. With so many modern bridges and pickups offering different spacing options these days, getting your alignment "just right" can be a headache—but it makes a huge difference in how your bass feels and sounds.

Why this gauge works:

Pick your Spacing:  Cormac talked to a bunch of fellow luthiers and narrowed this down to the four most common spacings: 17mm, 18mm, 18.5mm, and 19mm.
Equal Spacing: Most pickup manufacturers use equal spacing, not proportional spacing for their pole pieces, so that’s exactly how I designed this. It also means if you’re using the 6-string side for a 4-string bass, the math stays perfect.
Universal Fit: Cormac kept the gauge flat instead of radiused so it works on any fingerboard. Just measure two strings at a time and you’re good to go.
Stay Centered: It’s easy to get your spacing right but have the whole thing off-center. Center arrows were added on each side to help you line everything up with the neck and magnets.

How to use:

The notches on the sides are sized to fit your actual string gauges so the tool doesn't slip around.

4-String: Use the middle four grooves.
5-String: Use the larger hole to the right for a low B (unless you’re rocking a high C). Use your middle string as the center point.
6-String: Use all six grooves.

This tool is meant to be a solid starting point for your setup. If you like your G-string a hair closer or your B-string tucked in a bit, go for it! My only goal is to help you enjoy playing your bass a little bit more.