The 8.5mm soft steel screw tip drill bit with stop collar is used for plug spawn inoculations. The stop is machined on the drill bit shaft and the depth is set to perfectly match our plug spawn. A self-feeding screw tip pulls the drill bit into the log. This drill bit works best with drill tools turning over 2400 rpm and will be accepted into our angle grinder adapter to make drilling a breeze. Around 300 logs can be drilled before the bit will need sharpening. This bit is NOT covered by warranty when used in CORDLESS drills or angle grinders.