Why do most offstring yoyos use thin (M4) axles? Is it because they already use them for all the other yoyos? They are so much less durable.
An M5 axle will still fit within a c bearing, and a bolt will work even better.
Comparison:
yyt Spire will break after a few hours of play over tile, by running into chair legs, or by smashing into the stage.
yyf Flight (or yyt Airwave) will play fine after yoyoing over concrete.