The object pictured here (which you guys nailed almost immediately) is known as a boring bar [insert drinking pun here], which is used on a metal lathe to cut the inside of a part. I use this tool less frequently than most of my other lathe tooling, but it is nonetheless indispensable. More about what to do with this sucker after the jump.
In my post about vernier calipers, I highlighted one rugged option for making highly accurate measurements. When building projects that involve things like sliding fits, interference fits, shafts and bearings, rotating parts, measuring sheet metal thickness (and the list goes on, and on), accurate and repeatable measurements in the range of 1/1000 of an inch become very important. In this Tool School, I look at another option: the micrometer. A standard micrometer is capable of the same 1/1000-inch accuracy as the vernier calipers, and micrometers that incorporate a vernier scale are capable of measurements an order of magnitude more accurate: 1/10,000 of an inch. In addition, the variety of forms micrometers take allow measurement of a far larger variety of things than would be possible with calipers. Here's how to use one.
At some point, every builder progresses beyond the "eyeball it" method of measurement, and as you build more complex projects, the tape measure is often not precise enough. If you're assembling an engine or machining parts, for instance, you often need to be accurate to within a few thousandths of an inch or parts fail and bad things happen. Unfortunately, most of the tools that can provide this kind of precision don't survive well in a gritty, messy, all-purpose shop. Except the vernier caliper, a device that looks intimidating (especially to those who spy it in your shirt pocket) until you crack its basic code. Here's how to be as exacting as an engineer in anything you build.