Calipers are instruments that measure thickness and diameter. Gauges accurately measure everything from the size of holes in wood to the level of fluid in a container. A combination square can measure a 90-degree or 45-degree angle (figure A). It can also measure depth and distance, and a vial of liquid in the square can help the user determine whether a surface is level. An outside-measuring caliper measures the diameter of a cylinder. To use the tool, clamp it around a cylinder (figure B), and lock it into position. Use a ruler or a measuring tape to find the distance between the tool's two pointed ends (figure C) -- a measurement equal to the cylinder's diameter. A scribe measures diameter inside a hole and permits the user to trace a hole of the same size on a different surface (figure D). The inside-measuring caliper measures the diameter of a hole. To use one, place the tool's two end points inside a hole and stretch them until they touch the rims of the hole (figure E). Then use a ruler to measure the distance between the end points (figure F). The distance is equal to the diameter of the hole. The taper gauge consists of several rulers of various sizes used to measure the depth of holes (figure G). To use the gauge, slide the ruler into the hole until it can't go any deeper (figure H). The corresponding measurement with the top of the hole indicates the hole's depth. This tool is useful for determining the appropriate bolt size for a given hole. The dial caliper and digital caliper measure length with precision to the thousandth of an inch (figure I).
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