In the UK styrene sections and sheet, both Evergreen and other manufacturers, seem to have always been sold in 1/1000s of an inch (normally referred to as thou, e.g. '5 thou sheet'). This is despite the UK being theoretically metric for the last 35 years or so. I'm not sure how it works in mainland Europe, whether the actually sizes are different or the non-whole number metric equivalents are used. I've never seen it sold as scaled down prototype sizes, possibly because the main scale isn't H0.

Tim David