I have a set of SL BS64 on my Stumpjumper that I run in friction mode. In index mode the right shifter has 6 clicks, which I took to mean it's 7 speed, although it doesn't run through the 7 speed cassette very cleanly. I'm really a friction guy, so I haven't tried to fine-tune the cable tension, but figured if I did it would probably work fine. For reasons I'll explain shortly, I looked up the shifters, and from what I can tell they are supposed to be 8 speed. So I start counting fingers and wondering how 6 clicks gets me 7 shifts, which, according to my calculations, is how many you'd need to run through an 8 speed.
But wait, I'm not done. I needed another set of bar ends for a project and picked a set of SL BS50 on Ebay. Velobase lists these as 7 speed, although mine (unmounted) in index mode only has 4 clicks. What's up with that? The Ebay auction described them as 5 speed, but as far as I know Shimano didn't make 5 speed shifters, at least none that look like these (other than the model number ID, they look identical to the SL-BS64).
Based on my reading so far, I would have thought that the BS50 is a 7 speed shifter, and the BS64, an 8 speed, but my experience doesn't seem to align with that. I am further confused by the fact that Jenson lists the SL-BS50/SL-BS64 as if they are indistinguishable, and 8 speed.
My Stumpjumper has in fact a 7 speed cassette (and a Deore RD). The other bike I'm working on has an 8 speed cassette (and an XTR RD). So if in fact I have 7- and 8- speed shifters, I might as well put them on the correct bikes, in case I decide to index them. If all else fails, I can always run both sets in friction mode and not worry about it.
If someone is familiar with both shifters, I'm all ears. Thanks.