I had to drill and tap two holes for 3/8-16 screws in a hard steel ball joint that was too big for my drill press. At first I tried hand by eye and failed miserably. I bought a set of two drill guides and tried again. I attached the pilot drills (I used both pilot drills) with a C-clamp. They worked fairly well, keeping the drill bit perpendicular to the workpiece. In my case they would work better if they were twice as wide to make it easier to keep the guide perpendicular to the workpiece. However, they do not work if only a narrow guide fits. And you would have to buy four guides; two wide guides and two narrow guides. So there is a trade-off: use narrow guides and be more careful about positioning and holding the guide. The material used in the guides was not damaged (or worn) by the titanium coated HSS drill bits I used. I suspect they will work well for me for many years. Yes, I recommend them.
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