Would be worth carefully rounding the corners of ye home-made wrenches with emery paper on a flat surface, lest sharp corners became scrapers when in use. The relatively few times I've used such things I've noticed they have a tendency to rock or get out of alignment as we attempt to rotate, when held between thumb and forefinger.

If you're only rotating a fraction of a turn this isn't so relevant. Sometimes though, things that seem very tight give way and next thing you know, you've @#($%* up the slots. Set into a wooden handle they are much easier to keep aligned IMO.

And old utility scraper could be a good start for such a tool if the blade is of the right thickness.
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