a very nice 3/8" OD, perfect for threading 3/8x24 National fine thread. The 5" "target" barrel protrudes 2" out of the front of the slide, and the barrel swap is a snap. Shorten it to 3 3/4", and you have a nice accessory. Problem is, the lug underneath the barrel, which fits the cross pin in the frame, is made of zinc. So it probably wouldn't take many barrel swaps to wear that contact area to the point of looseness. Having to drill out the "complications" and bury a $130 gun, along with its $50 spare barrel and accessory, wouldn't be that big a sacrifice, though. Ditto a spare barrel for the Browning Buckmark .22.