Some types of depth measurements are easier to take than others. While you can slide the rule of a combo square down into a mortise to find the bottom, how do you do that with a small diameter stopped hole? A Snap Depth Mini Depth Gauge (iGaging, $25 in 2011) makes the task, well, a snap. Use it to measure holes, dovetails, slots and grooves, rabbets ... you name it. The device has a slender, spring-loaded probe. Zero it out with the tool’s base pressed against a reference surface, then slide it over the hole to take a reading. For holes deeper than 1", you get 1" and 2" extension rods to expand the depth-finding range to 4" overall. Here’s a bonus: the Snap also has a mounting lug on the back that could be attached to a separate base. That way, it can double as a dial indicator for evaluating shaft runout, blade flatness or other tasks. Quite versatile.