Somebody here recommended doing repairs at home with the bike toolkit just so you know you have what you think you have. Good idea.
While out riding, I suddenly remembered leaving the right TB locknut loose so stopped to fix it. The 10mm wrench would not fit! I had to ride home without fixing it.
Back home I measured the wrench at 9.92mm. The 8mm on the other end measures 7.96mm.
It's always been my assumption that fasteners are made very slightly undersize and I know that tools are made slightly oversize. IIRC Proto tools were pretty sloppy. My good 10mm at home measures 10.2mm.
Check your toolkits guys, specially you off roaders.