This style is referred to as Calipers. In will measure both "IS" and "OD" (inside dimension and outside dimension) .

If you do a search on Ebay for "Calipers" you'll find plenty of very inexpensive items to choose from.

Here's an example:

http://cgi.ebay.com/6inch-150mm-Digital-CALIPER-VERNIER-MICROMETER-GAUGE_W0QQitemZ160011727486QQihZ006QQcategoryZ64814QQrdZ1QQcmdZViewItem