The most popular bottom bracket version in 2010 has to be the Mid. Mid is basically a typical American size bearing, without the aluminum collar. Since the Twombolts use a 22mm spindle, our Mid BB is for a 22mm spindle. If you have a Mid BB frame and 19 mm spindle, you can get the American BB, and just remove the aluminum collars. The Euro BB only works with 19 mm spindles.