Thatīs a complete Mamod Wheel Ben, mounted inside an outer Wilesco rim 
Had itīs circumference maximized by a few layers of 3M electrical tape, to obtain a press fit within the Wilesco rim.
As the tape is narrower than the Mamod rim, that leaves an outer open gap inbetween the two rims, that i have just finished closing up with body filler.
I could as many others do, have thrown the Mamod wheels in the lathe, and shaved the rim down to the spokes, but like the fat wheel rim better, so opted for this approach.
I went to look and stock Mamod outer rims are quite skimpy looking but have the nice spokes and cast in bolt head detail. Also loose ground clearance if just mount stock Mamod so I really like your solution, think the beefy wheels set up will go nicely with my "big block" conversion, thank you!