This is a used Shimano Sealed Cartridge Bottom Bracket model BB-UN51. It is in good condition. The bearings are smooth and well packed. Model BB-UN51  BC 1.37x24  73 mm shell, 107mm spindle. There is some rust on the outer shell of the BB but it is only cosmetic and it does not affect the functionality of the BB. The left side cap is missing. Made in Japan.