Basically, thats the base plate, the design in the centre is a group of 4 concentric circles, 2mm wide, 2mm deep into a 3mm base, and 5mm apart, cut in with a lathe.
Circles @ 20mm diameter, 15, 10 and 5
The same set of circles is then cut in again, offset 2.5 mm to the right and left.
Single inlet over the core, then 2 outlets right and left, ala WW.
Any thoughts?