Where there's a need...

I similarly found myself short of the needed Allen key size to remove a (not 10mm, perhaps 12mm?) hollow bolt holding a freehub body onto some inexpensive(Fulcrum?) wheel.

I found that a 3/8" square-drive extension fit the inside of the 12-point bolt head snugly enough to apply prodigious torque sufficient to remove the factory-tightened bolt..

After considering having a decent batch of tools (fashioned from flat stock) made, to fit onto the eight-sided, 38mm Stronglight fixed cup, I instead found a 1-1/2" 12-point socket at the pawn shop that already had it's end ground square (the better to grab the thin, 8-sided flange).
The socket fit well enough to apply quite-generous torque using a 1/2"-drive breaker bar.
For giggles (and to fill in my ever-expanding socket-size inventory for use mainly on trucks),I later tried a slightly-smaller 1-7/16" socket that turned up at Goodwill, but which was far too small to fit onto the 8-sided flange.




On another occasion, wanting to remove the cogs from a Sunrace freewheel body, I needed a tool to engage at least two of the four spline lugs of the internally-splined lock ring.
I found it easiest to simply use the aft end of an old chain whip, narrowing the width slightly to perhaps 32mm or so.
Using a 12" Crescent wrench allowed application of more than sufficient torsional torque to the whip handle, while another, bigger chain whip held the outer body from turning.


On a related note, pounding in a slightly-oversized Torx bit into a blodgered hex socket opening can transmit generous removal and re-installation torque.

Going ever-further into left field, I found that a #12 SAE screw/bolt is a desired (only) 1/2 millimeter larger than a (stripped) M5 bolt hole, allowing for only minimal oversizing of the hole on your water bottle bosses or derailer arm.