Couplemate U bolts are tested and rated every batch. 1/2 inch U bolts are rated to 1500kg per axle. Heavier loads and off road campers should use 5/8 inch u bolts.
It is important to re-tension u bolts approx 100 kilometers after installation. U bolts are made from mild steel that stretches under tension and vibration until it settles position. It is not uncommon to see mild steel stretch 3mm without re-tensioning.
Couplemate testing has found Shock loading on the highway or in the paddock can put up to 3 times the rated loading onto the U bolt and that is 4500kg for a 1/2 inch U bolt.
U bolts and made from mild steel must be checked frequently. Mild Steel under tension has a habit of stretching causing your recently tightened u bolts to become loose. After tightening your u bolts for the 1st time, re-tighten the u bolts when you reach your first nightly stop.