I do believe that oil riggers use 'metric inches' for some things ie. 10" to the foot
Quite so; there are measuring tapes with 'big inches' ( decimal feet ) and 'little inches' ( normal inches ).
When reckoning the depth you have drilled, you tally up the lengths of the joints of drillpipe you have run in hole.
It's easier to tally it up in your tally book in decimal feet.
The oil industry is dominated by the US, and also by units that are of practical use.
eg: fluid densities can be in PPTF: Psi Per Thousand Feet; the hydrostatic gradient they produce.
All tubulars are in inches.
Drill bits, hole diameters etc are in inches.
Pressures are in PSI.
Acoustic slownesses in microseconds per foot.
Rock densities, are, however in g/cc.
Resistivities in ohm-metres.
Some units are just plain made-up.
Natural background gamma radiation is expressed in API ( American Petroleum Institute ) Gamma Ray Units ( gAPI ).
The definition of this unit is "1/200th of the difference between the activity of 2 lumps of concrete in a test-pit at the Uni. of Houston".
ETA: A reference for that:
http://www.glossary.oilfield.slb.com/en/Terms/a/api_unit.aspx