Brass Shim Thickness: Imperial and Metric Sizes Explained
Understand brass shim thickness with an imperial-to-metric table, measuring advice and checks for choosing individual sheets or a shim assortment.
When buying brass shim, thickness is the dimension that makes the adjustment. Sheet width and length determine how much material you receive, but they do not tell you whether it will produce the required spacing. Start with the measured correction and the assembly’s specification, then compare the thickness options.
Imperial brass shim is still useful for older drawings and machinery. Understanding its metric equivalent helps when your measuring tools or supplier listings use millimetres.
What is brass shim used for?
Shim stock is thin material used to provide controlled spacing or adjustment where the design calls for it. Brass is one option among several shim materials. Select it against the application’s requirements, including loading, environment and whether the shim must remain stable in service.
A loose joint, damaged surface or incorrect component does not automatically become suitable for repair by adding shim. Establish what the adjustment is intended to change before choosing the thickness.
Imperial brass shim thickness in millimetres
Multiply inches by 25.4 to obtain millimetres. A “thou” is one thousandth of an inch: 0.001 inch. The conversions below are calculated values, rather than a statement of any supplier’s sheet tolerance.
| Inches | Thou | Millimetres |
|---|---|---|
| 0.001 | 1 | 0.0254 |
| 0.002 | 2 | 0.0508 |
| 0.003 | 3 | 0.0762 |
| 0.004 | 4 | 0.1016 |
| 0.005 | 5 | 0.1270 |
| 0.008 | 8 | 0.2032 |
| 0.010 | 10 | 0.2540 |
| 0.015 | 15 | 0.3810 |
You may see 0.002-inch brass shim described as approximately 0.05 mm. That is a rounded conversion. It does not make it exactly the same nominal thickness as 0.05 mm shim. Whether the difference matters depends on the adjustment and the tolerance required.
Nominal thickness and tolerance are different
The nominal value identifies the thickness being supplied. The tolerance describes the permitted variation around it. An exact unit conversion does not remove that variation.
Check the actual material specification rather than borrowing a tolerance from a different supplier or alloy. If the adjustment is critical, measure the piece being installed and establish whether your measuring equipment is adequate for that task.
Specialist shim thickness selection guidance similarly emphasises measurement, material choice and tolerance. Those checks belong together: thickness alone is not a complete selection.
Measuring thin shim sheet
Use an instrument with suitable resolution and repeatability, such as an appropriate micrometer. Clean the measuring faces and the sample, and use consistent measuring pressure. A burr, fold or trapped particle can matter when the whole sheet is only a fraction of a millimetre thick.
Measure at several undamaged points if the condition is uncertain. Keep the original label with the sheet and mark the remaining stock after cutting, so the next project starts with a known thickness.
One shim or a stack?
A single suitable shim can simplify assembly. Where the design allows layering for adjustment, check the combined measured thickness and how the layers are retained. Avoid treating a nominal stack total as a verified installed dimension.
For a simple calculation example, 0.003 inch plus 0.002 inch totals 0.005 inch, or 0.127 mm nominally. The actual result depends on both sheets’ thickness variation and the assembled surfaces. This arithmetic does not establish that stacking is acceptable for your mechanism.
Record which layers were used, rather than leaving an unexplained stack for the next maintenance job.
Choosing a brass shim assortment
An assortment can be useful when several projects need different adjustments. Compare the thicknesses included, the sheet dimensions, material specification and quantity per thickness. A larger pack is only helpful if its contents match the work.
For a repeat job with a known requirement, a refill of the correct sheet can be more economical than another complete assortment. Store sheets flat and protect them from damage during handling.
For a broader list of items worth labelling and replenishing, read our essential workshop consumables article. If you are selecting thicker bar stock rather than shim, our CZ121 vs CZ108 comparison explains why the material grade matters alongside the dimensions.