A while back I wanted some U-bolts for a project I was considering that were very similar to what you are looking for. With some creative queries on Amazon, I found them. There were differences in the length of the threaded portion, length of the leg, material diameter, etc. that I had to try. But, through trial and error, I eventually found some that would work.
Sherm & Terry w/rescues Steve (std Poodle) & Eydie (min Schnauzer)
2015 Jay Flight 27RLS (Camped: 102 nights 2015, 90 nights 2016)
2006 Ford F350 6.0 PSD, Lariat, 4WD, CC, LB, SRW, auto., Camper pkg.