I found this tool amongst all my tools, some of which are more than 100 years old. This one says patent pending and the was patent was issued in 1955 to LNL products. Assuming they didn't just leave "patent pending" on it after they received it, it would put this tool at between 1952 and 1955. So, what is it for?
It was used to measure pipe diameters, both inside and outside, as well as wall thickness. The small jaws at the lower right can measure thicknesses up to 1/4" in thousandths. Here is a picture of me testing it on a drill bit.
I then measured it using my electronic calipers. The calipers read 3.2mm, which is 125.9 thousandths, which is pretty close for something I am holding with one hand. I did it again on another tube with both hands and it was dead on. Impressive. You can also use the small jaws for measuring pipe wall thickness.
The ruler that comes out the top is for measuring larger outside diameter pipes. In order to obtain inside diameters, you must measure the outside diameter and subtract the wall thickness x 2. The ruler on top turns out to not be as accurate. I measured this pipe end and it said 21/32" (656/1000s) while my digital caliper read 686/1000s.
They do have a convenient conversion chart on the tool for 32nd to thousandths since that is what you are measuring with the pop-out ruler.
Pretty nifty little pocket tool!
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