I purchased this rod to use as a squib rod, primarily. For those unfamiliar with that term, a squib is bullet that gets stuck in the barrel of a gun due to insufficient propellant (powder). At 0.3125" diameter, this rod will work perfectly in any 9mm, .38 Special, .357 magnum. It will also work fine in larger calibers like 40 S&W and .45 ACP. The 12" length is perfect to ensure that even super long handgun barrels (like some long revolvers) can benefit from its use.