Sorry, just saw your edit.
The boss is the protruding cylindrical part that comes on a lot of sprockets. It's a good wall thickness on the 40T sprocket which made drilling and tapping for grub screws nice and straightforward
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The tether is in the rules so that if the axe head becomes separated from the arm, it doesn't go flying off, potentially breaching the net roofing of some live arenas and into the crowd. At least, I think that's the main reason. It's more for axe heads that are bolted onto arms where the chances of the bolts shearing is reasonable, but on Onyx the axe head is welded on, so it's a bit redundant, but dems the rules![]()
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