When I made my MV2FS ready for home-use, I also added a ball top to my Neo Geo CD Controller Pro. This was supposed to be handled in an article in 2018, but it somehow got lost. Anyways, here it is:

The SNK Neo Geo CD Controller Pro (aka kidney bean stick) doesn’t have a regular ball top like the arcade stick. Instead, it has an indented head, probably to rest your thumb on.