It guides your flywheel onto your shaft. Full stop
November 3, 2022
taco eater :
Dan from Stratford, CT United States
This key fits fine into the super stuffy race crank, where the original Puch key needs just a hair sanded off it to fit.
As others have said, lap your taper. This guy does not hold the flywheel in place against the crankshaft, all it does is make sure your flywheel is going on in the right direction.
If you hold your engine with crankshaft vertical, it can be tough to get the flywheel on without this thing falling out of its slot and needing to be fished out of the case from behind the stator. Make gravity be your third hand, orient the crankshaft horizontally and turn it so the key's slot is facing upwards. Place this key into place and bingo, your flywheel slides over without pushing the key out of slot.
Now DON'T FORGET TO TORQUE DOWN THAT FLYWHEEL NUT!
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Get two
November 27, 2021
taco eater :
Moped Madman from Murrieta, CA Independent Kingdom of Treatland
Never know what could happen, i installed one and stupidly didnt beat the flywheel on hard enough and it sheared the key in twain. Miraculously it didnt reck my new crank's keyway or the flywheel but it did cause me alot of suffering, get two and even if you dont need both its good to have an extra, and dont be afraid to beat your flywheel on like its the commie that shot your grandpa
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lap your damn taper and torque to spec
June 17, 2021
taco eater :
Dan P from MN United States
Flywheel woodruffs have one purpose: to help you line up the flywheel when installing it. The do NOT prevent the flywheel from spinning on the crank. That is what your lapped taper is for. If you are shearing these it means you do not have the flywheel properly seated on the crank. Lap your taper (YouTube it ffs) and torque to spec. Don't blame the woodruff for shearing, it was never intended to stop the flywheel in the first place!
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I sheared 2 of these.
September 5, 2020
taco eater :
Matthew Mulligan from terryville, CT United States
I wouldn’t trust them, definitely lap the taper if you run one.
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Shear Shear shear
February 18, 2020
taco eater :
Reed Hois from Downers Grove, IL United States
I've probably bought 15 of these and they keep shearing. I have a CDI and I keep the flywheel on tight but i cant go more than 20 minutes without a problem :((
It guides your flywheel onto your shaft. Full stop 
I sheared 2 of these. 
Shear Shear shear