I'm working for UMBC lab peoples; they needed a means of attaching specialized grips to a PlayStation controller they rigged for their wheelchair.
I designed this replacement joystick with attachments.

Ball Attachment 2 has a flat top for easier printing.

Ball Attachment 3 has a rounded top.

Ball Attachment 4 has a rounded top, but the ball is increased from 1" to 1.5" in diameter; likewise the height of cylindrical portion has been increased by the same ratio (1.5).

DO NOT PRINT THREADED SIDE DOWN; YOU RISK THE THREADS NOT TURNING OUT WELL ENOUGH TO WORK