Originally Posted by
mactec54
You need to have 1-1/2 times the diameter of the capscrew (SHCS) you are using, so would need to have 9mm for a 6mm capscrew, (SHCS), most who are doing this weld a flat bar of steel on the side or inside the Rectangle Tube, the surface is then machined, for the rail to mount to
Either way you do it you need to machine the surface that the Rail will mount to, if welding to the out side, stitch weld the bar where the mounting holes for the rails will be, the bar needs to be wider than the rail so when it is machined you can machine a shoulder on it for the rail to sit on, if putting the bar inside the Tube you only need to tap the bar and weld it in place at the ends