I can attest to what Bob has said. The EXACT same thing happened to my '69 about 4 years ago. I had just returned from a 300 mile trip to the U.P. in Michigan for the St. Ignace show. On the way back, I had burned a collector gasket, so the next day, I replaced it, took it around the block to check for leaks, pulled into my driveway and BANG!! The driver side front dropped onto the frame and skidded to a halt. When I got out to survey what had happened, the front tire was sideways, and had wiped out the front fender!. Upon further investigation, I saw the nut from the lower balljoint laying on the ground, I picked it up and to my surprise, it was totally clean on the inside, smooth, the threads were gone. I checked the ball stud and guess what, the threads were still on the stud, in the grooves. Needless to say I was not happy. After a brief stint as an Engineer for TRW Steering Systems, I realized that this is exactly what will happen if the nut does not go through the proper heat treating process. I guess I was the unlucky one to get this lemon part, and my car paid the price. (The only good thing was the insurance company wanted me to pay for the new balljoint and installation, and they would buy the new panels and pay for bodywork, I convinced them that the only defective part was the nut, and I only had to pay $0.59 cents!!!) I only thank God that this thing didn't let go at 65 mph on I-75 the day before.