My late grandpa’s soldering iron’s handle has found its way onto my Miata with the help of a 10x1.25 nut glued into the bottom (hole enlarged with a step bit). Test fit it on the Miata and it doesn’t knock into the radio like I thought it might and is surprisingly ergonomic, but it’s ludicrously light-weight. Probably going to fill it with ball bearings and glue (so they don’t rattle) to add weight

Comparison with my previous shift knob, the stock knob from my 1991 Miata