Adjustable bottom bracket

A component of a bicycle through which the crank is mounted. It has two bearing cups on either side. One cup is fixed in place while the other is removable or adjustable. This is the older type of bottom bracket before sealed cartridge bottom brackets became prevalent. The adjustable bottom bracket requires fixed and adjustable cup tools to properly tension the bearings. The bearings are not sealed, but they are easily accessible for cleaning and lubrication.