Review on 🔧 Alfa Tools FB61493 Forstner Drill Bit Extension by Darion Wooten

Actual 10mm (0.394") not 3/8 (0.375) which really is a big difference. When used in a drill press with a 3/8 Forstner In shank, a 10mm hole will cause the long extension eccentric to spin uncontrollably unless used at low speed as the drill bit will offset .019". is. My drill chuck actually came off my press because of the vibration and my new Freud bit fell tip first into the iron base with the weight of the chuck and extension behind. Otherwise a quality product, well finished, you just have to be aware that it is actually 10mm.