I make custom powder bushings for "0", "00" 1/2" and 5/8" powder slides. In each case the bushings are 1/2" in diameter. I also offer the powder slides that use the bushings.
Hornady used to produce "Pistol Powder Bushings" in 22 different sizes. These bushings were also 1/2" in diameter and required a 1/2" powder slide. You can still find some of them around, but the last time I checked they had disappeared from retail outlets.
Bruce Williams