THESE ADAPTERS DO NOT FIT COTHRAN TUBES. HE MAKES HIS TUBE-THREADS TO TIGHTER TOLERANCES THAN CROSMAN/BENJAMIN DOES. WE MAKE OUR ADAPTER THREADS OVERSIZED TO FIT CROSMAN/BENJAMIN TUBES TIGHTER. HIS TUBES ARE TOO TIGHT FOR OUR ADAPTERS.
This is our original Long Magnum Tank Adapter, it mounts tanks up to 4.5" OD. It threads directly into 7/8" OD Crosman/Benjamin tubes including 2240, 2250, 2260, 2300KT, 2400KT, Discovery, Challenger, Maximus, Fortitude,1701P, 1720T, Marauder Pistol and many related models with the same size tubing and thread size. A 7/8" OD shroud or muzzle brake has about 1/4" clearance with a 4.5" OD tank.
You can either drill the anchor-screw hole in the tube as described in the next paragraph or install it with threadlocker on the threads instead. The anchor-screw is the safer method and is recommended if you plan to pressurize the tube to more than 1200 PSI. It will thread past the point where it's straight so you thread it all the way until it touches the tube, then back it off a partial turn until it's straight. If the anchor screw is in the correct location it will be straight with the screw lined up with the hole. With threadlocker you get it straight with the tube lying on it's side and leave it until the threadlocker sets. Only use a tiny bit of medium-strength threadlocker or you will never get the block out without damaging it and/or the tube. A heat-gun may be needed to remove the block after the threadlocker has set, only heat enough to be able to turn the block, the less heat the better. Do not use a torch or any heating method hotter than a heat gun, the tube can lose it's structural integrity if heated too much, heat evenly around the diameter of the threaded sectiion.
MARKING THE HOLE LOCATION: Thread the adapter all the way in, then back it out until it points straight down. Mark the center of the hole 1" from the back of the block, not the front of the tube. Deburr the inner edge of the hole after drilling so the o-ring on the adapter doesn't get damaged during installation. If using the harder 90D o-rings, which it comes with, you need to tap the front of the block lightly with a rubber mallet, block of wood or your hand to get it started into the tube without pushing it past the anchor-screw hole, then push the o-ring under the edge of the hole with a small slotted screwdriver to prevent it from being cut. The screw is T10 drive with a head diameter of .271". The hole should be .275" - .281" (9/32) to fit in a recessed fashion like PCP valve screws do.