Old 03-30-20, 03:59 PM
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The first type, "block tooth" is really a sweeping generalization.

Very early freewheels were near this, but even those had a bevel on the face side much of the time.

Then, one must recognize Regina and the Atom, dimension equal to them.
bevel and a divit along the top of the tooth, probably to assist the chain or prevent the chain from shifting, your choice
These were decades in the manufacture.

Shimano then arrived at the twist tooth to work with its Uniglide chain. Circa 1979.
Did not really catch on, chains had a bad rep for stretching.
I tested one for Shimano, and it lasted a mere month. I stretched it out, about 1,500 miles.
Their engineers were not happy.

So it goes.
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