Builder’s Bog is intended to be no harder than wood. It is also designed to cross link and bond with cellulose. I do not feel it is a good candidate for the repair you envisage. I think an epoxy resin would be more adhesive, harder and better able to hold a thread if this is what the fill will be required to do.

I suspect the knob isn’t a “poly-type” plastic like polyethylene or poly propylene because these are not heat resistant enough. They are also almost impossible to adhere to due to their waxy like surfaces. The knob is more likely to be a phenolic like bakelite. An epoxy like Knead It from Selleys will work best. Or if adhesion to the glass lid is required a two pack liquid epoxy.

Regards
Stuart Jordan
Managing Director
(13.4.2020)