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Dyna Drive ®
From WikiPedalia
In the early '80's, Shimano introduced a special crank/pedal set, which used much larger diameter threading where the pedal screwed into the crank. This allowed the bearing to be built into the inside of the pedal thread, eliminating the need for a pedal axle. The purposwas to improve the biomechanics of the pedal by placing the bottom of the foot below the pedal axis.
The threading chosen was 1" x 24 tpi, same as a standard 1 inch headset, except that the left side was a left thread.
This was rather a good idea, but never caught on.
