A piece of 2" x 4" timber is still referred to as "2 by 4" in the UK, except it now measures 50mm x 100mm (actual conversion is 50.8mm x 101.6mm, the difference

A piece of 2" x 4" timber is still referred to as "2 by 4" in the UK, except it now measures 50mm x 100mm (actual conversion is 50.8mm x 101.6mm, the difference being moot when building scale is taken into account)