Used as an idler pulley. See http://dkprojects.net/belt_drive_brompton/
The center of the pulley is designed as a press fit for a metric ball bearing, 22-mm O.D., 7 mm width. In one printing press fit worked perfectly, in another it was a little loose -- I added a brass shim.
4.72 w x
4.72 d x
1.858 w x
1.858 d x