Okay, it’s a “u-bolt”. It’s a u-bolt with a flat radius to distribute pressure over a wider surface to minimize crushing. It also resemble a u-joint u-bolt…
But what is the technical definition/term for this style of u-bolt?
I’ve tried; u-bolt; flat u-bolt, strap bolt, axle bolt… the website this image was found on is for boating accessories, this is what they term a “frame u-bolt” but nothing else like it comes up when the term is googled.
Size-wise… looking for approx. 6mm diameter x 65mm length, with 50mm throat… ish.
They seem similar to U-joint mounting bolts found on a lot of old (maybe current too) vehicles. You can find them all over under the names of u-joint bolt, u-joint strap, u-joint retainer or u-bolt retainer. I am not sure where you might get them in mass quantities other than from an auto parts supplier though.