I have used them and they DO work great.<BR>I highly reccomend them.<BR>There is no need for more than one manndrel because the tap itself is the mandrel. The mandrel has two precision, hardened then ground tapered bushings that fit into either ring of the receiver.<BR>I have found this system to be as accurate as single point cutting the threads.<BR>If you are going to purchase this tooling, I would reccomend that you get the thread and lug reccess reamer as well as the bolt face tools. If anything, the bolt face tools are just fantastic. They totally assure you that the bolt face is in line with the bolt bore, wich after trueing the action IS in line with the receiver threads.<BR>NOTE:<BR>This system will not work for a barrel set back, as it cuts the threads 1 1/16 + .010<BR>I have built rifles with this system, as well as single point cutting and could not tell a bit of difference in accuracy, except this system is quicker.<P>For more info conact Dave Manson<BR>Manson reamers 810-953-0732<BR>...Celt