This "made for the mushroom industry" 13.5mm soft steel screwtip drill bit with stop collar is used for sawdust spawn inoculations when using any of the Okuda inoculation tools. The machined drill bit stop sets the depth to match the tools' volume resulting in properly filled inoculation sites. A self-feeding screw tip pulls the bit into the log. The 13.5mm drill bit is best used with drill tools turning over 2,500 rpm and has excellent performance in our angle grinder adapter. This bit will drill about 300 logs before it will need sharpening. This bit is NOT covered by warranty when used in CORDLESS drills or angle grinders.