Here's a little tip if these things jam on the shaft.
Don't try to punch the shaft through the coupling from the side with the set screw.
This only makes it mad.
Push or punch the shaft from the side without the set screw
-or-
Push on the coupling from the set screw side.[b]
In other words ......
The shaft needs to move toward you when your looking at the side of the hub with the set screw.
Confused yet ?
