55-up 12 volt flywheels have 168 teeth. A 6V starter armature has approximately a 5/8" diameter shaft and straight drive lugs that engage with the drive unit. 12V armature shafts are approximately 1/2" in diameter, and the drive lugs on the shaft and in the inside of the drive are spiral which makes the drive unit turn a little as it engages the flywheel teeth. This minimizes the tendency of the teeth to jam together instead of meshing.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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