If you know anyone with a surface grinder, you can just grind down to whatever width you like in a matter of minutes.
Just a parallel grind, and the only rake is a front one if using on brass or ali, but a bit of top rake as well if using for steel. I normally put one on either end of a bit of tool steel, just in case you break it (very rarely), then it is just a matter of flipping over and carrying on from where you left off.
My most used one is 0.025" by 3/8" long, and could part off 1/2" diameter bar with no problems. But I have made grooving tools as narrow as 0.010" and 1/4" long with great success.
Just two things to be noted. The tool has to go in perfectly square to the job, and after say 100 cuts in non ferrous, it might be time to make a new one. Because of no side rake or clearances, the width actually wears away, so if you have an old one, it is best to check the width before use.
Hope this has been of some use.
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