When I first started making finger-tops, I made them from a single piece of wood, which included the tip. But after talking to collectors, I found that they really wanted a tip that would stand up to heavy use, as well as add "bling" to the look. So I switched to steel ball bearings, stone and other hard materials. A lot of high end CNC machined metal finger tops use ruby crystals for tips. The tip material I like best are small stone cabochons (rivets) used in leather craft, like these: Stone RivetsDo you buy the tips or make them yourself?
I don't have any strict rules for finger top design...whatever looks good works for me. The only thing I really pay attention to is trying to add some kind of texture in the upper handle area, so you get a better hold on it when giving the top a spin.Those are works of art for sure! Is there a ratio that you follow for the proportions?