I have strung a certain customer's Black Knight Max Force 970s 3 times in the past month with Ashaway 70 and 67. This racquet has a warranty tension of 36 lbs, I have strung them at 27 lbs each time. He has broken them at the top one or two strings from the centre of the mains all within the same day of returning. I have a Pro's Pro Challenger with an attached 2086 WISE Tension head. I assumed they had been mis-hits due to the positioning of the string breakage. Initially I was wondering if it may have been my stringing technique. I have strung a different customer's Black Knight Max Force 970s at 28 lbs and it has been a month without any breaking of the strings. I string my Black Knight Max Force 930s at 25-26 lbs and they have been durable. All racquets mentioned were strung with Zymax 67/70. A friend suggested it may be the grommets that are causing the break but if the strings are breaking well below the grommets at the top area of the strings, I assume it would be a mis-hit. Either way this is not good for the customer or myself, I am not sure what the cause is! Please help!