The shaft end is M5-.8 according to the metric guide at Home Depot.
And skateboard bearing barely fits in a 3/4" PVC pipe. It needs shaving to fit but it will.
A Maglite Mini head is the exact diameter of the skateboard bearing on the outside. Forturnately there is no way to shave the inner cavity to make it fit. Use PVC or find another flashlight to use. The brinkmans are too large and the electronics are not easy to get out.