Square or round leaf spring U-bolts… What trucks used them?

[derotoreut]

I posted this in the suspension forum, but couldn't get anyone to bite on this one. I'm sorry for listing this again, but I'm trying to get an answer.

I see that some of the trucks used square rear leaf spring U-bolts and some used round U-bolts. in the 67-72 truck years, what were used and when? I'm curious because I'm installing a Skyjacker lift on a '70 K10 and they sent me square spring mounting bolts, but my rear axle was installed with round U-bolts.

The first picture shows the new U-bolts for both the front (rounded) and rear (square). The rear U-bolts on my truck are round as can be seen by 2nd pic.