With all due respects Robert,
You have to be joking.
While it is not good engineering practice to use imperial tools to set metric clearances
Go back and read your own specifications
0.15mm +/- 0.02mm
Or
0.0051181102" to 0.0059055118 " to an absurd level of accuracy
So you are trying to tell us that 0.0001 " is going to put a mower engine out of spec ?
No two mechanics would set a tappet to within that accuracy every time
This is the reason why kettering ignition systems switched from points gap measurements to points dwell angle.
Even if the poster bought a 10「 set of feeler gauges which might not have a 0.006" leaf all have a 0.001" leaf and when I went to school 0.001 + 0.005 = 0.006
I know using more than 1 leaf is not good enginering practice, it will suffice for a mower engine
By virtue of listing a feeler gauge specification the systematic error is + or - 1/2 the smallest increment .
So the listed clearences are 0.15mm +/- 0.02 mm to withing +/- 0.005mm
Most of the feeler gauge sets I have here go up in 0.001 increments for imperial or 0.01 mm for the metric.
Measurement of less the 0.0005" with any feeler gauge are not reliable due to operator variances which is why we use plastigauges for vital clearances.