Do you have a feeler gauge? If not, you should consider adding one to your tool kit.
A feeler gauge is set of reference tools for measuring the widths of narrow gaps. It’s a sort of go-no-go tool, where you try different gauge blades until one fits.
They come in different styles and sizes. Shown here is the Proto J000AA, which has 25 blades 1/2″ wide x 3″ long. The sizes range from 0.0015″ through 0.040″. Each has both inch and metric-equivalent markings.
The blades can be removed if needed, but it’s usually not necessary.
I recently had to level the wings of my new table saw, and used feeler gauges along with a straight edge and rule to ensure everything was within tolerance.
In this image here, a 0.040″ (1.02mm) feeler gauge slides freely in the gap between the extension table and a straight edge. It’s out of spec, and the company wanted image confirmation that the gap is larger than 1.0mm before they could send out a replacement.
Feeler gauges can be stacked together if needed.
I consider this to be a toolbox essential, even if it’s not something you use everyday.
Pricing can vary depending on size and blade count.
The Proto J000AA can be purchased for under $20. It’s made in the USA.
If you want something less expensive, the Gearwrench 161D 32-blade feeler gauge is under $12.
Feeler gauges are also available with bent angles or tapered tips. My stance is that, unless you know exactly what you need, it’s best to start with a straight blade set. Most thinner gauge sizes have some spring to them, where angled tips could be convenient, but not essential.
Inexpensive feeler gauges – the kind that sell for $5 at online marketplaces can be useful as shims in a pinch.