For easy to drill and there's no need to push the bit.
The flange could fix the depth of hole and each of hole are the same.
It's used in planting the mushroom in the wood cultivation.
Size: Overall Length Twist Length Shank Diameter
8~12mm (Japan) 75mm 25mm 6.35 impact Hex
17~19mm(Taiwan) 90mm 50mm Round Shank