Doubts

I don't understand "this is where we're gonna go"? to do what? It's really unclear. Editing- In second though maybe He just saying "Now we are talking about this part of.. axes..?

What is "Keyed"? in "that pulley is keyed"?

Switching the belts is real simple, this is where we're gonna go to the axes and lawnmower blades. You push in, turn right, that pulley is keyed, So it won't snap back at you, until you want it to...

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