This tool accomplishes a goal that few other tools can: copy bigger complex contours. Place the Duplicator against any curvy contour with the arrows visible and pointing to the contour. Carefully transfer it to the medium (or even a scanner) and again, draw on the arrow side. Works a treat if you are quite handy!

V2: I have added a thinner bolted version where you can adjust the friction between the links and tighten them up if they wear over time. This needs m3x12 countersunk bolts (standard would work as well). It will still work on friction alone, but because it is thinner it will deform more easily without the bolts. If you have these bolts I highly recommend to use the V2 version.

Some things to keep in mind:

1. It's flexible, both when posing and drawing so take care to hold it down properly and not put too much force against it. The longer you make it, the harder it gets to handle. 20 links is quite doable, mine is 42 links and can be harder to transfer.

2. It has a 0 tolerance friction fit, which should be perfect. But to be sure: print two to test, snap them together, wiggle a bit and see how the friction is after a while with your printer, filament and settings. Up the extrusion multiplier (in the slicer or on the printer) to increase friction.

I used PETG since PLA can deform over time more easily.
Other that that, happy printing!