The "loose fit" "tightens" up a bit after tinning both interior surfaces of the monoblock, and the exterior surfaces of the barrel stubs that fit within the monoblock. W. Ellis Brown, who wrote his book on converting double shotguns to double rifles, taught us to use both half and half, more or less, threading and soldering, barrels into monoblock. Some guys use only the threading, and others use only the soldering; no threading. All work well, and have plenty of strength for purpose intended. When only soldered, the large overall surface area soldered, provides more than enough overall strength for this purpose.