Another term used to describe a type of Bottom Bracket is "Cup and Cone" which has adjustable loose bearings. They are adjusted using the adjustable cup (on the non-drive side) which has a lock ring to hold it in place after the bearing adjustment. The oldest type of Bottom Bracket system still in use is called an open bearing system. Cotterpin and Cotterless Bottom Bracket’s come in to this category. (The term "cotterless" simply describes the lack of a cotterpin).

Main Parts

  1. Bottom Bracket spindle
  2. The fixed cup (drive side) - as it name implies - is fixed into the frame and is not adjustable.
  3. The adjusting cup (non-drive side) on the other hand can be tightened or loosened to make the Bottom Bracket run perfectly smoothly.
  4. Bearings.


The bearings in an open/loose system can either be individual loose bearings or housed in a bearing cage. Either way, the bearings will run inbetween the cups and cones located on the spindle.


The advantages of an open bearing system are that a mechanic can strip out an open bearing system and then inspect the individual parts. If necessary, the bearings can be serviced, cleaned and re-greased - or even replaced, without having to replace the entire Bottom Bracket unit.


The disadvantages are that the Bottom Bracket unit is not as well sealed against the elements and will need to be serviced more regularly to work in an optimal fashion.


Common cotterpin sizes are 9.5 mm for British, Asian and most German bicycles. French and Italian often use 9 mm, or sometimes 8.5 mm. Sometimes you may need to file cotterpins to fit.

BB Spindle Interface

Cotterpin cranks and BBs are the old-fashioned way of fixing the crank to the BB axle. They use a wedge-shaped (cotter)pin with a nut on one end which secures it in the round crank hole. This then fits onto the spindle as shown.

Cup Sizes

These are British ISO and Raleigh 1 3/8" X 26 tpi

WORKSHOP TIP: With these sorts of BBs it is advisable to practice degreasing and cleaning fairly frequently as preventative maintenance.

Back to overview