38 Special / 357 Magnum, This unit has a screw on barrel with a "barrel lock" so it won't loosen from vibration. Choice of 2 safety's. Hairpin or thumb nut. Which ever the user prefers. Has a spring loaded firing pin, can be mounted on a speargun shaft. 303 Stainless Steel, 6mm Mount Threads ***** Rod & Ball Assembly Sold Separately ***** POWERHEAD WEIGHT: 6.0 oz.