an indy fab fixxed, a soulcraft s/s, and a host of others
is it a bottom bracket similar to this?
if so...this set up lets you run a splined crankset (has a stiffer interface between spindle and crankarm) on a sturdier bb than before. in days past, bottom brackets had a square tapered spindle (as pictured above) and the spindle fit nicely in two sealed bearings in your bb cartridge, which then threaded nicely into your frame. then companies decided that some modernization was necessary so they designed a splined bb spindle for a stiffer crank/spindle interface. only problem was that the outer diameter of the bearings remained the same to fit in the cartridge (and frame) while the inner diameter was also increased to make room for a larger diameter spindle. this made the bearings thinner, which made them more likely to crap out on you over the course of a few months. the next "innovation" was to move the bearings out of the bb shell, which enabled manufacturers to use a larger sealed bearing without regard for the confines of the bb shell. one minus is that these bearings sit outside of your frame, exposing them to the elements, so while they may not wear as quickly, they can get gummed up in particularly nasty conditions. phil wood has come to the rescue effort by bringing cyclists everywhere their infamous bearings that can be retrofitted into your existing bearing cups...giving you a silky smooth crankspinning feel for years to come...well, not really...but for a good long while.
of course, if your bottom bracket doesn't look like this, feel free to disregard everything i've said