Having the right fit is best for magazine loaders. The ST6 fits the popular .380 ACP for most models. The ST3 used to do a pretty good job, but with the popularity of the new smaller handguns improving, the demand was so great that this has become on of our most popular models. If you have a flat in line magazine from back in the WW2 era or one of the newest brands, the ST6 does the trick in 4 easy steps.