Do you realy need to thread the monoblock? I think the most common way is to solder the tubes into the monoblock, beeing carefull to pre solder the block and barrels first offcourse.

The thing i heard is that if you make a sharp edge or cun into the barrel or block it will take less force to break it. It appears that to regain the strength you would need to add a lot more material (diameter) to compensate for the weakening. Its as if you take a rod and make a cut into it it will break at the cut if you bend it much sooner than a rod thats smaller in diameter and with no cut made into it. And a solder joint should be sufficient to hold it into place.

But i think somebody will tell you that treading is the only way to be safe. He would also be competent to calculate the streangth of the bond if you state the diameter and lenght of the monoblock. Yeah, and also i mean real solder the low temp stuff.