Making a Unique Tool. You Can’t Buy This Anywhere!

[BuffaloJohn]

These things are called Trammel Points and have been around for ages (some references go back to the 14th century).

Trammel Points are used to make Beam Compasses. Some attach like the ones this guy made, some use the thinner flat of the ruler, some are quite large.

And - you can buy them many places - amazon, ebay, McMaster, dozens of woodworking tool stores, home depot, and Starret has half a dozen:

https://www.starrett.com/products/pr...mmels/trammels

Here are some from MicroMark which calls them a Yardstick Compass:

https://micromark.com/products/Yardstick-Compass