The BBT-18 is a heavy duty, investment cast tool for installing & removing the following eight-notch bottom bracket cups: Shimano Octalink- right cup with external notches ISIS Drive The BBT-18 has 8 notches with an outside diameter of nominally 43.4mm. The inside-to-inside width is Approx. 38mm. Each notch is Approx. 3.9mm wide. The hole in the center of the casting is 22.5mm, & will not fit over the 30mm spindles.