Im not sure. Take a look at The Venolia Catalogue why would they use imperial mesurements all the way through then go metric when detailing the Piston clearances.
as far as i can figure 0.010mm is not 4 thousandths of an inch
1 thou...0.001"
1" (25.4mm) / 1000 = 0.0254mm
so
4 thou....0.004"
0.0254mm * 4 = 0.1016mm
and
10 thou...0.010"
0.0254mm * 10 = 0.254mm
is this right or am i confused????