Let me start by saying that I only used 4.5 and 6mm drill bits. As you can see in the picture I "done" drilled the already drilled hole for the aircraft cables. I started drilling holes with the drill bit that came with the cable box and it worked great. I then bought these scrap pieces to go over the last 1 1/2"-2" of 6x6 treated lumber. The 4mm drill bit on the left of the picture just twisted out when I pulled it out, so I switched to the 5mm drill bit, which twisted so hard it broke off in the pin. In general, do not buy them, you can seriously hurt yourself.