I have made odd ball adapters by moulding fimo modalling clay in an oversized slip on, and then letting it dry. It shronks a bit on drying. Then I wrap the affair with teflon plumbing tape, mask adjacent aras with masking tape, and apply slow setting hot melt glue to the area needing the snug fit, and push the metal thing with undersized clay bit over and leave it there until the glue dries.

Peel it off, remove masking, and trim up the overspill with an x-acto knife, than make it look pretty with a black sharpie marker.