Since it seems I'm the only person on these forums with any real experience with these, I figured I'd spread the wealth and give you guys some more detailed info on Vise's new interchangeable thumb product, the IT.
Here is the actual removable slug portion of the thumb, complete with a white plastic screw base.
http://img70.imageshack.us/img70/1096/thumbslugbasebt7.jpgHere is the thumbhole where the slug base screws into the ball.
http://img70.imageshack.us/img70/7075/baseinstalledry4.jpgThe thin black ring around the top of the thumbhole provides support and consistent spacing so the slug fits each ball the same.
http://img70.imageshack.us/img70/1628/ringinstalledinthumbholmz8.jpgThe base is secured in the thumbhole of the ball with both glue on the plastic base, plus a molly that is expanded and glued into a smaller hole drilled inside the thumbhole. Here is a picture of a base and slug screwed together before being installed:
http://img67.imageshack.us/img67/3724/slugbeforeinstallationws1.jpgAnd for comparison's sake, here's the Vise IT slug (right) compared to the Turbo Switchgrip (left)
http://img67.imageshack.us/img67/8512/viseitvsturboswitchgripfj3.jpgHere's a crash course on how it's installed (but PLEASE carefully read the directions Vise includes in the kit, this is just a quick overview. It's really simple once you figure it out, but you need to make sure you follow the directions exactly as Vise has written them!)
After marking the grip center line, drill the hole at the size indicated in the instruction manual for the size thumb slug you wish to use with the kit's included drill bit (and bevel the edges a little to prevent cracking, of course) You will ALSO drill a smaller second hole inside this. This hole will acommodate the molly. It needs to be exactly 1 inch deep for the IT to fit properly. (Sorry I didn't get any pictures of this part)
Install the black plastic ring in the top of the thumbhole
http://img67.imageshack.us/img67/8867/insertspacerringintothuwy0.jpgThe kit comes with a tool to install the base -- it's essentially a hollow slug with a T-shaped handle on top.
http://img70.imageshack.us/img70/3706/installedspacerringmollpp4.jpgAfter you do a test fit to make sure everything is OK, spread some glue over the white plastic base and the molly
http://img70.imageshack.us/img70/8382/gluethemollyandbaseqd5.jpgPlace the base and molly in the ball, aligning the slug with the grip center line.
http://img235.imageshack.us/img235/687/placebaseinstallationtosj2.jpgAs the glue is setting, drop one of the small molly extenders (not pictured, they look like a small plastic peg) into the hole in the handle of the installer. Use the included tool that looks like a screwdriver without a bit to gently hammer the molly extender into place. (Sorry I didn't get any pictures of this part either)
Once the glue has set after about 30 seconds or so, you can unscrew the installation slug and remove it, leaving behind the base and molly. The ball is ready for use now if you already have the thumb slug drilled.
Now, as for drilling the actual thumb slug, Vise includes a special bowling ball just for this. Place the ball on the press and drill the hole with zero pitch.
http://img70.imageshack.us/img70/6868/drillingtheactualslugkf6.jpgAfter the thumb is drilled, you can then place it in the ball, lock it into place, and cut down on the slug to make it level and work out the thumbhole as necessary just as you would do with any regular thumb slug.
