I want to pick up a tool for installing GXP bottom brackets, which have external bearings and require a tool with 44 mm od and 16 splines. The same tools reportedly work for many Shimano external bottom brackets and other brands.

Park Tool makes the BBT-9 and the BBT-19.2. The difference is that the 19.2 is a cup-type tool that allows the use of a torque wrench, while the BBT-9 is an open ring that doesn't take a torque wrench. I have read in several places that the cup-type tools tend to slip off BB bracket easily, marring it and potentially damaging the notches. (The SRAM/Truvative version of the tool reportedly has the same issue). I would prefer not to do that, but as a home mechanic, my arm might not be well-enough calibrated to get the torque into the right ballpark just by feel.

Here are links to the tools:

Bottom Bracket Tool - Park Tool

Bottom Bracket Tool - Park Tool

I can probably get someone to help hold the bike while I'm torquing the BB, so I can concentrate on holding the tool in place, but it would be nice not to worry about it in the first place.

Any tips or thoughts on this? Maybe slipping isn't that much of an issue, or maybe I can just crank it down tight with the other tool and not worry about getting the torque perfect?

I have a Shimano tool that is similar to the BBT-9, but open ended. I have never worried about the amount of torque on the bottom bracket. I put lots of anti-seize on the threads and run it in till it contacts the bottom bracket face, then just tighten a bit more. I have never had one come loose.

A steel tool on an aluminum cup will usually mar the aluminum cup, but its just cosmetic. If you want no scratches on the cup, use some sort of buffer like a piece of thin cloth or tape between the tool and the cup.

I put a bar clamp across the BB tool, torque wrench and across to the other side. This holds the tool securely in place so I have both hands available for the wrench and to brace the frame and there is no risk of the tool popping off and damaging anything..

That's an idea. It seems like it would be a little difficult to clamp securely (without popping off at the wrong time), but I can think about it. Maybe I'll make a wooden accessory so there will be a flat clamping surface on the drive side....

I have the bbt-9. I torque it until the knurling for the plastic pentalobe shimano hollowtech II driver on the other end digs into my palm and hurts. Hasn't let me down.

I figure with [english] BB's you've got precession on your side tightening as well.