The flange has two pentagonal holes to hold the filament ends.
The flange and barrel have a screw of M36.
The inside of the barrel is carved with a hexagonal groove inscribed in φ22 mm.
Option
This model is a P-5 bobbin of the Japanese Cable Makers' Association Standard (used for enamel wires, etc.) with the flange thickness and barrel width cut in 1/2.