This is the one Screw I do have, and I suspect that the Screw which holds the Sprue Plate was major diameter at the top to oblige the size of the Screw Plate Mounting Hole, so, at least at a glance, I expect two Screws were not the same at their upper shank part.
I might just see about finding some other 'Modern Bond' Mold which is for a Boolit I can enjoy and use, and I can just borrow the Screw from it, when wishing to cast with this Mold.
https://media.fotki.com/2v2HQUSNox9J4Vm.jpgHosted on Fotki