A stencil to create circles on a ¼" isometric grid. The circles fit in N by N squares (where 1 ≤ N ≤ 8). Also functions as a straightedge.
100% infill is recommended.
If you would like to design your own, the OpenSCAD module I created is included in the files. Note: the module is two dimensional, so you will need to use linear_extrude(h).
Cross-posted on Thingiverse.
The author hasn't provided the model origin yet.