Unfortunately the tap on the second hole broke. At first a hole worked like a charm. I used an HHS 5-M 08 mild steel tap. I used cutting fluid with a Milwaukee M12 drill driver. I don't know what I could have done differently to prevent a breakage. Like I said, great concept, it just doesn't seem to work in the real world. Maybe someone with less experience has better luck, but this 90-year-old retired electrical engineer and handyman couldn't get them to work as intended.