Jon that is a very good question.
When I made the winder I put aluminium blocks on either end of the shaft
and I screw wooden plates to them to mount the bobbins. I thought if I needed
different mounts for different type of pickups that wood would be a lot easier to
make for centering a specific bobbin.
The picture is off a P-90. Notice that there are two flatplates (bobbins) the old style has the plastic.
I'll be using the "new" style -fiber.
I'm sure it's just the flatwork with spacer that will be mounted. I'll screw it to a new wooden mount
that will be screwed to the aluminium block. ( the maple mount will be used for all P-90s)
The spacer is super-glued to the flatwork and after cured a bead of super glue is applied all
around the spacer to prevent the wire from getting between it and the flatwork.
I thought when when I was building the winder that not all bobbins would be flat on the bottom so
I wanted to use wood to modify as needed....turns out I was right. Easy to screw the bottoms to wood too. lol
Why? Because I'll then have winding experience for the Strat and Tele single coils and the Gibson P-90.
From there....double coils starting with the mini-humbucker. For a good reason if one should like to guess.