Because nothing is ever exactly 8mm. Well, nothing they could afford on the mass production scale they use to produce trucks. So they have to build in some margin of error and allow that some axles may come out a little larger and some a little smaller.
If they chose to tell their axle manufacturer to make 8mm axles, some would come back too large and the bearings wouldn't fit on!
So they have to pick a number that is smaller so that for sure each axle will allow a bearing to slide on.
Pacifica, CA
"the pen is weak. skateboarding is as deadly as all hell" - gonz
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