A blank disk that can be used to fit a 24mm axle on a BB386 shell without a BB. 

This can be used for transferring bike fitting dimensions to a a frame without the installation of a bottom bracket. Maybe you want to get your dimensions dialed in before your new BB shows up. 

Depending on how accurate your printer is, it can also be used to check the bore or roundness of a bottom bracket shell in order to troubleshoot manufacturing defects. I was able to get this down to a 10µ diameter deviation, this should be good enough to troubleshoot most issues with BB shells.

The fitting is tighter on the shell but looser on the spindle. 

This is not meant to replace a bottom bracket with bearings.