Hi
As long as the load is not that great, one can whack
out the center with a drill and then notch it with a file.
Rather you than me. This gear is about 1/8" OD (that's from memory,
whatever you do, don't make one on that spec :-)). I would not fancy
trying to file internal splines on a hole about 2mm (i.e. the 'root'
diamater of the gear) in diamater...
-tony