I just had the same problem with the Spring Eye Bolt from Classic. They were very accomodating to replace them...now reading this post I see it's a problem they have known about for at least 4 years.
and I am not talking about ancient Chinese sailing vessels. I am in the process of doing a frame up restoration of my '52 GMC 1/2 ton and wanted to give a heads up on some quality/fit issues with a couple of our parts suppliers in case anyone else has ordered these parts.
I ordered new spring shackles and spring eye bolts from Classic Parts of America. No problem with the shackles but as I was in the process of torquing the last of four spring bolts to 80 pounds of the 60-80 foot pounds recommended in the shop manual, the bolt head snapped off. In looking at the bolt where it broke off, it had a very grainy appearance which leads me to think it was cast rather than machine from a billet or bar. These bolts are Classic part number 74-057 and have a raised heart shaped leaf on the head of the bolt. They were $30 each. As I contemplated what to do about it, two more broke off overnight without me even touching them. I contacted Classic about the problem, and they offered to send me four more, but after considering something as important as this critical suspension part, I decided to go with bolts manufactured by Rare Parts that I found through O'Reilly Auto Parts. At over $45 each I hope these are better quality. Classic said that had a report of the same problem a while back but thought it had been corrected. They are sending me an RA to return these parts for credit.
I also ordered a completed new braking system including master cylinder, stainless steel lines, hoses and wheel cylinders from Jim Carter. As I installed the master cylinder, lines and front hoses and wheel cylinders everything appeared to be fine. I can't say enough about the good quality/fit of the stainless lines. They came in a box labeled Inline tube. As I got to the rear of the truck my problems began. The single brake hose from at the rear would not screw in brake line running down the side of the frame. The steel line has a 3/8 X 24 male fitting which is correct; however the hose had 7/16 X 20 male and female fittings on both ends. I compared the new hose to the original that was on the truck and the original had a male end fitting that was 7/16 X 20 and female fitting that was 3/8 X 24. I am not sure the country of origin for this hose (it didn't say) but it is definitely manufactured incorrectly for this application. This is Carter part number ME136 which based on their description is correct for my vehicle. When I tried to install the rear wheel cylinder (their part number ME323) the wheel cylinder block attaching bolt would not screw all the way in. The packaging for the wheel cylinders stated that they were manufactured in China. With the two copper washers installed it still lacked almost 1/16 of an inch from tightening all the way. The bolt bottomed out in the wheel cylinder before tightening. These were new bolts from Carter, but I compared them to the original and they were the same length as the original so the problem was definitely with the wheel cylinders. I talked with Jimmy at Carter and got a RA to return the hose and wheel cylinders to them for a refund. I have since located these parts also at O'Reilly and they are manufactured by Wagner - hopefully here in the US.
Long story short - on something as critical as the suspension we are better off buying from name brand US manufactures than than no-name Chinese junk.
