Starrett designed the almost 4″ jaws and 3mm diameter tips of their new 5006BZ-14/350 electronic groove calipers to measure the width of internal and external grooves. The caliper will measure outside grooves from 0″ to 12.5″ and inside grooves from 1.654″ to 15″.
They manufacture the calipers from hardened stainless steel and the tips can be installed facing in or out or to measure either outside or inside grooves respectively. The calipers read with a resolution of .0005 of an inch or 0.01mm.
One cool feature is these calipers have a standard RS-232 interface rather than the cryptic protocol many other calipers use, so you can connect it directly to a computer with a serial port. When either a serial cable or their DataSure Wireless Data Collection System is attached, the in/mm button sends the current measurement.
The calipers come with a wooden case and one CR2032 lithium battery will power the calipers for a year of normal use. No word yet on how much these calipers will run.
Groove Caliper(pdf) [Starrett]