The wiring sizes in the diagrams of our BMW manuals are stated in millimeters. Go figure... actually.
A page in a site I keep bookmarked is
http://onlineconversion.com/gauge_wire.htm. I've been attempting to create my own little chart of millimeter v wire gauge as available here in the USofA. Of course, the wire gauge conversions are as close to mm as is available locally.
Knowing that there's someone on the R65 forum that can confirm my data, here's what I've got as a start. Please check my "guesstimates" and add corrections and/or additions as necessary. Thanks.
0.75mm = 21ga (Lots of this size wire on our bikes)
1.0mm = 18ga
1.5mm = 14ga
2.5mm = 10ga