Originally Posted by
Jeff Wills
FWIW: back before STI/Rapidfire, Shimano offered the Deore and Deore XT front derailleurs in "Alpine" and "Half-Step" versions. As you'd guess, the Half-Step version had very little difference between inner and outer cage plates, while the Alpine was designed for 10-tooth difference, typically a 26/36/46. This made it tough to keep all of the versions straight: Half-Step vs. Alpine, 28.6 vs. 31.8 vs. 34.9mm clamps. This was in the 1988/89 timeframe:
http://www.mombat.org/Shimano.htm#1988
That's an interesting bit of history too. The last half-step capable fd's I have personal experience with were a Sun Tour ARX that came OEM on a 1985 Bridgestone 400 and a Shimano 600 (pre-Ultegra, pre-indexing) that I installed later on the same bike.
I used them with a 46/42/26 triple SR crank and a 13x28 6-speed freewheel. The gear chart showed a nearly uniform progression of ratios with no duplicates over the entire range of the two larger rings.