I set out to make a yardstick adjustable trammel set using as many parts 3d printed as possible.  I hope to make another version using some standard hardware, but this one only requires 1 nail, with the rest all printed.

The set consists of two trammel ends.  One uses a nail as a pivot point and the other is adaptable to a range of pencil sizes.  The nail side is designed around a 2" long #6 nail (.110" diameter)  The pencil size uses a set of 3 wedges to lock various sized pencils or marking devices in position.

Update: 5-29-23

There is now an alternative STL file for the the trammel end sized for a larger diameter object such as a sharpie marker.  Unfortunately with the wedge design, the sharpie version will not adjust small enough for a pencil using the wedge design.

The yardstick I used was .24" thick x 1.375" tall.  The design has room to accommodate a range of yardstick sizes.  As long as they remain under .25" thick it can handle a height of 1" to 1.5" tall.

All items should import in the proper position for printing, but if not should be oriented as shown below.  The nail is pushed in from the top and is captured in the counter bore on the trammel end.  It should be a very tight fit and will probably take some light hammer taps to get going.