Heavy Duty, Grade 8 Round U-Bolts. Not the cheapest but the best.  They're also not a one size fits all.  There are 7 sizes available.

• 5/8" (0.625") diameter Grade 8 Steel
• Rolled Threads for extra strength
• Threads are 5" long so they will fit! Cut off what you don't need after they are on.
• U-Bolts are sold separately.
• Each U-bolt includes 2 Tallnuts and  2 Thick laser cut 1/4" Washers.

Sizes

• PN: UB275 - U-bolt, 5/8" x 2 3/4" x 10" - Typically used on Dana 44.
• PN: UB325 - U-bolt, 5/8" x 3 1/4" x 10" - 3.0" OD axle tube: Dana 60, Ford 8.8
• PN: UB338 - U-bolt, 5/8" x 3 3/8" x 10" - GM 14 Bolt axle
• PN: UB358 - U-bolt, 5/8" x 3 5/8" x 10" - Pumkin side of a Dana 44
• PN: UB378 - U-bolt, 5/8" x 3 7/8" x 10" - Pumkin side on a Dana 60
• PN: UB300 - U-bolt, 5/8" X 3" X 10"
• PN: UB418 - U Bolt, 5/8" X 4 1/8" X 10" - Dodge Dana 60 front axle at the housing