Microscopes and optical tables in the US use mixed units. For example, you will often get a product marketed "25.4mm" which is 1 inch. Frequently a single optical table will mix components between imperial and metric.

You can see some of the approaches here: https://www.thorlabs.com/tutorials.cfm?tabID=4068826A-1CD4-4...

(I work with CNC and I spend much of my day converting between inch and mm).