U-bolts are what provide the clamping force needed to hold your springs to the axle. Any movement in the center bolt area can cause a spring to break so follow your manufacturers recommendations.
If that is unavailable, use our recommendations your springs will thank you.
Remember, torque your bolts to the recommended specifications immediately upon installation, and re-torque the U-bolts after 50 miles. and then again after 500 miles.
And heck, it’s a good idea to check them every time you’re underneath your vehicle. Remember, tight U-bolts will extend your spring’s life and performance.