Jeroen used an 8mm shank rotary broach from Polygon Solutions Inc. to test his home made broach holder. The whole story is captured at Home Model Engine Machinist website.

Polygon Solution's Rotary Broach in home-made Broach Holder

The 8mm shank broach is held in the 10mm bore using a sleeve. Standard hexagon and square broaches are available from Polygon Solutions for immediate delivery.