Since I bought my stringer last October (Eagnas Combo 710, a dropweight with fixed clamps and 6 point mount), Ive mostly strung my racquest with Natural Gut mains and Isospeed Pro Classic crosses. For the most part Ive had no issues and Ive used the following varietys of Gut with no problems: Pacific Toughgut Pacific Classic Pacific Imperial (my favorite, too bad it's discontinued) Global Gut (17 gauge in black) I use the KProOpen racquet which has main tieoffs at 6B, and cross tieoffs at 5T and 12B (which is the 3rd cross from the bottom). This weekend I reluctantly decided to cut out my last Imperial Gut setup which had been strung in late April because I had a indoor match coming up and I always have issues with my serve going long when I have a old setup in a indoor match in the middle of the summer. I only had 3 half sets left: Pacific Primegut (I have yet to get this to work, although the first time was with no grommets, it does seem very sensative though) Pacific Classic Global Gut I started stringing the Primegut. I did the mains and tied them off with what I thought was no issues. Then I did the Isospeed crosses from the top, got all the way to the bottom and clamped the last cross (which goes over where one of the main tieoffs are). Then when I tightened the knot for the cross, I heard a "CRACK", and then seconds later the main in 6B snapped right at the main tieoff. I proceeded to string the Classic and something similar happened again. This time I heard a "CRACK" when tying off the last cross, but only a couple strands of the main broke off. It seemed more like it was scored right where the fixed clamp intercected it then necessarily on the main knot. I took it off the machine and about 10 minutes later the main snapped. Which leads me to wonder: 1) Was this gut maybe of poorer quality? 2) Did I pull the knots too tight and weaken them. I did use my hand but I did also pull them tight enough to try to pull all the slack string thru. Maybe I would be better off just securing the knot and letting that slack string tighten up when I remove the clamp? The weird thing is the other main string at 6B doesnt break though, just the one on the same side as the cross tieoff. 3) Is my fix clamp drawing back and cutting thru the mains somehow? It seems hard to avoid drawback on the last cross. I went to the Global Gut the next day and it worked just fine. But this time rather then pull really tight to cinch the knots for the mains I just pulled tight enough so it was secure around the string and I let the slack tighten up on it's own when I released the clamp. (which actually is more like I did most of the other jobs, it's a new phenomenon where I pull extra tight) Any ideas?