DrillSteady fits a 9/64-inch drill bit for a No. 8 screw or fastener. The drilling tool's unique design allows faster, more accurate drilling on round tubes in installed frames, corners, or anywhere. The drill guide opens to clamp onto the tubing and holds the drill bit in place securely. It features large, knurled thumbscrews for a sturdy grip. Use DrillSteady Drill Guide #3587 with 3/4" to 1-1/4" tubing.