I recently was asked to repair a decorative windmill for a friend. One of the vanes was missing. I needed to know what gage the steel vane was so I could make the missing vane and its weight would be the same as the others, lest it run out of balance in a strong wind. The procedure outlined here works also for determining the gage of wire.
Needed: I do not have a micrometer. I used a machinist's clamp and a feeler gage set. You also need a sample piece of steel or wire you want to size.
Step 1: Place the Clamp
Attach the machinist's clamp to the steel or wire you want to size. As best you can, make sure the jaws of the clamp are parallel to one another when the clamp jaws are tightened.
Step 2: Measure the Gap
Place blades from the feeler gage set into the gap between the jaws as close to the steel or wire held by the clamp as possible. In this case, I was able to slide two feeler gage blades into the gap. The two together amount to 0.026 of an inch.
Search the Internet for <wire gage size>, like this one: http://www.efunda.com/DesignStandards/gages/wire_forward.cfm Enter the thickness of the piece as you measured it. The web site will tell you the gage or the range of measurements for each gage.