Yesterday I was doing a bit of testing regarding threaded holes for 5mm screws in Delrin (aka POM, acetal) and found that a 3/16" drill bit drilled the perfect size hole that when given a slight nudge, a 5mm screw would enter the hole and form its own threads in the plastic along the way. The threads formed in this manner were actually giving me a better, more solid grip than I was achieving through traditional tapping. Well, last night after having spent a couple painstaking hours tapping the ends of all my ox extrusions, I began to wonder why I hadn't tried the earlier experiment on aluminum. To make a long story short, it not only worked, it worked exceedingly well and had I considered it sooner I could have reduced a couple hours of hand tapping to just a few minutes of drilling. The grip on the screws was firm and tight and while it loosened a slight bit after a few rounds of threading/unthreading it still felt tighter than the hand tapped holes. An attempt at levering out the screw was unsuccessful but with 14mm of the screw embedded in the hole this result was pretty much expected. If you've got a lot of holes to thread whether they be deep load bearing holes or shallow end cap holes, you might give this method some consideration. I know my M5 tap won't ever see the light of day again. _______________ Conditions of the experiment: 3/16" Dewalt titanium coated bit in battery powered hand drill, Tap Magic cutting fluid, black 20x40 extrusion. Disclaimer/Safety Recommendations: Your mileage may vary. Always test first using non-critical parts. Use a cutting fluid or oil to reduce wear on cutting tools. Always wear safety glasses. _______________ Update 4/16/15 For screws gripping into delrin (pom) 11/64" (0.1719" or 4.37mm) seems to have the best grip. For screws gripping into aluminum plate, #14 wire gauge bits (0.1820" or 4.62mm) seem to get the best grip and reusability. Threading oil was helpful. For screws where grip is not important like end caps, 3/16" (0.1875" or 4.76mm) holes are more than adequate. Where grip is important, use screws long enough to get at least 10-12mm threaded embedment.