From page 30 of AWSA Tech Controller's Handbook. "The handle or handle assembly shall be made of 2.5 cm - 2.8 cm (1" to 1.25") outside diameter material with no sharp edges or projections, and it is recommended that it shall float."
I have measured many handles at R tournaments, and never knew, or was asked to check handle diameter. And, no doubt there were some skinny handles, 0.940 or 0.888's. First question, does anyone really ever check something so silly as this? Second, why is this even in the rules? So long as bottom of handle to inside of end loop is 1.5 meters, what does it matter? Maybe a relic from many years ago when bent handles might have been a safety concern? At least for ML handles today, same thick wall aluminum core no matter what handle diameter you use.
Obviously, I'm bored this evening....