If you were to go to a Drafting store or drafting supply house, you would be able to get a thre sidded rule, It would have a side that is broken down in 10ths. If you have a caliper that should help you see how much this is also.

.10 or.100" = 1/10" = 2.54 mm

.125 = 1/8" = 3.175 MM

http://www.industrial-enclosures.com...alculator.html

I love your title, metric/standard help , I hear you load and clear!