Big Al is right. That is how some attach. But since I cut these to match, there is the .125" wall tube that is thinned further on the lathe. Then I spin an internally threaded nut with a smoot od that will allow tube press fit over the nut. Once pressed on and ensured it is true to the barrel I drill a hole from the tube into the nut and heliarc th hole shut. This locks the two together permanently and very solidly. I then turn or file or sand the top of the weld to make it disappear. Then I torque the tube barrel and receiver to spec, mark the location of the gas tube, remove, drill one hole for the gas tube then reinstall. Done.