Weld-on hubs from Koch Industries have a black oxide finish. Used to attach pulleys or sprockets to shafts.
Black oxide finish
Furnished with standard keyway and two set screws
Comes in 3 sizes labeled by series:
• V Series = 1-1/8″ Outer Diameter
• W Series = 1-5/8″ Outer Diameter
• X Series = 2″ Outer Diameter
Used to attach pulleys or sprockets to shafts