After finishing this much I realized how bad I am at measuring and reading numbers. The mystery device is a pipe bender I fashioned from a couple cut-off bits from a 2x4. I cut an arc that I approximated from several different radii. I then carved a 90 degree grove along the center of the curved edge. This was a clumsy process that involved chisels and an angle grinder, but years of ice carving more than prepared me for the subtleties of carving a small groove into an old 2x4. To avoid collapsing the tube I also packed its end with nails while bending it.

The second image is the fork ends domed into this shape so the bits fit into it.