Remix of https://www.thingiverse.com/thing:1622868. Dimensions should be identical to the original, aside from differences in chamfer/fillet.

Printing:

Print with 0% infill and 3 perimeters (e.g. 1.2mm shell for a 0.4mm nozzle). The chamfered side faces the print bed to avoid elephant-foot issues.

Test without calipers:

Print two of the item. They should fit together well. Loose fit is underextrusion, tight fit is overextrusion.

Test with calipers:

The distance between the inside of the forks should equal the width of the other end (nominally 10mm). If the inner measurement is larger it is underextrusion, if the outer measurement is larger it is overextrusion.

There is a spreadsheet by https://www.thingiverse.com/gork at https://goo.gl/kbuZMi that can be used to calculate the proper extrusion multiplier based on your caliper measurements.

Other:

I have included the FreeCAD file.