IDEAL Industries Serrated Combination Flexible Bit x 54"

The 54 inch working length is what electricians use to reach down a wall cavity from a single cut-in and bore several studs or plates in one pass. On a standard 16 inch stud bay layout that covers roughly three bays without a second opening. The flexible shank is what lets the bit bend into the cavity through a small hole.

No. It is a wood boring bit, described for easy to tough wood only. For steel studs or block you need a different cutter, not this serrated combination bit.

The head has ultra-sharp ground threads, so it self-starts and bites aggressively rather than skating on the face of a stud, and those threads give it pulling power to work back through obstructions in the cavity instead of binding.

Both are offered, and the choice is about how much cable you plan to pull through one hole. The 9/16 inch (90-073) gives more clearance for stacking or for pulling multiple runs; the 1/2 inch (90-070) removes less wood from the stud. If you are standardizing one bit for general residential rework, the larger 9/16 inch bore is the more forgiving hole.

No. The bit is a one-piece flexible combination bit at 54 inches, so the flex shank and cutting head are the same tool. You only need a drill that accepts the shank, plus an alignment or retrieval tool if you want to steer and pull the bit out of a wall cavity.