Designed to adjust the adjusting cup in an open type bottom brackets. Some adjusting cups, instead of having a machined outer edge (normally 17mm wide), have holes in the outer surface of the cup. Apart from these holes the entire surface is flat and no other tools but the pin spanners can be used to turn and adjust the cup. The number of holes in the cup varies from 2 to 8, so does the diameter of their layout therefore pin spanners are designed to expand or contract to fit in the opposite 2 holes of the cup. The pins on theses spanners are also different in shape and sizes to facilitate the myriad of cup standards in the market.
