Sram pressfit 30 to bsa adaptor kitgenuine replacement upgrade pressfit 30 to bsa adapter bicycle bottom brackets connect the cranks to the bike and allow the crank arms to rotate there are various sizes of bottom bracket shell on the market so compatibility needs to be checked the three most common frame bottom bracket shell widths are 68mm english threaded road and mtb 70mm italian threaded road and 73mm british threaded mtb there are also many axle shapes and styles from jis or is