I only had to drill 4 holes 2" deep. I was able to drill all 4 holes but 3 of the drill bits are now unusable and bent as shown in the picture. The 2 bits on the left in the picture were never used. I drilled through a hard concrete wall with an SDS Plus drill bit. The tips of these curved baits are fine, only the shaft of these baits is not hard enough. Structural steel. Beware!