Originally Posted by fietsbob

TA .. manufacturer of chain rings and cranksets, french.
square taper ,the meeting of traditional BB axles.

Shimano's indexing stuff is trademarked as STI

traditional friction shifting by hand shifted past the cog slightly
and then you pulled the lever back a little , to center the shift mech over the cog.

the index stuff got pickup ramps , pins and shortened teeth,
so the mech only goes from over one cog to another .

relies on the careful adjustment and alignment of the drive train as the segmented detents .. klicks,
on the lever and the pre determined motion of the derailleur sideways have to be just so..
and need synchronizing.
front lever and rear the shifter .