I have a cannondale touring style frame from the 90s that i'm building up and the bottom bracket cable guides that I bought do not fit the frame. The screw doesn't even fit the frame.

That made me start to wonder, why are there waterbottle like bosses sticking out on the bottom of the downtube near the bottom bracket? What's going on? Are those for some special bottom bracket guide?

That's for carrying your camping fuel, e.g fits into a bottle cage that can be mounted there.

wow. that's pretty cool!

I still don't know what the deal is with the bottom bracket thread size. isn't this thing supposed to be standardized ?

Some Cannondales do have their own BB cable guide. Yours might be one of the lucky ones.

i think you may be right bob. the guides that i bought curl upwards, but on the frame there's this extra weld that joins the chainstays further outwards... crap!

Cdale cable guides are proprietary and snap into the non-threaded hole in the BB. Alternately, You can use a very thin nut along with a bolt to secure it.

might not fit in with a cartridge bb