This fixture is used for indexing work using a vise and square for 5, 7, and 9 sided polygons. See the remix link for the even-sided polygon version of this tool.
FAIR WARNING : I did not attempt to print out this re-mix, although I expect it will work as well as the even-sided version.
A commercial version of this tool for even sided polygons (and a useful how-to video) is here :
https://www.lakeshorecarbide.com/14-1rangerose-index45-60-90degreeindexingblock.aspx
There are large (diameters up to 50mm) and small (diameters up to 25mm) versions of this print. Each print needs to be tapped for the appropriate size setscrew as follows :
Ideally a brass-tipped setscrew should be used, but alternatively a brass or aluminum shim can be used to prevent the setscrew from marring the work. Remember that these are plastic and do not over-tighten the setscrew; use it only to hold the fixture in place, and not as a clamp.
The OnShape 3D CAD files for this are here:
Print in PLA using the 3mf files provided; otherwise :
In addition, for the larger size I used a modifier block to increase the perimeters around the tapped hole to 5, for additional strength.
The author remixed this model.