I've been finalizing my decisions on shackles and thought I'd bring you guys along. I've got a background in engineering projects that involve rigging, so it's a big deal to make sure I'm at least in the realm of being safe.
Here's some great baseline information about 4x4 recovery:
Pirate4x4.Com - Extreme Four Wheel Drive
I have ultimately selected 5/8" Crosby 209A shackles. First off these are US made and have an actual weight rating. Here's a link to the sizing info:
Crosby® 209A Alloy Screw Pin Anchor Shackles - The Crosby Group
I selected the 5/8 shackle because it's rated at 11,000 lbs in a straight line pull, with a factor of safety of 4.5. This pairs nicely with my 10k winch capacity for straight line pulls. For 45 degree pulls you reduce capacity to 70 percent and 90 degree pulls by 50 percent. This is a bit of a compromise, but since there's a 4.5 factor of safety, my risk of failure is pretty low.
Here's a side loading chart:
https://www.google.com/url?sa=t&sou...FjAEegQIAxAB&usg=AOvVaw2VkDw6feeaI0c748ZkKRKc
When using shackles, it's also important that the load is spread evenly across the shackle pin. In my case, for a 5/8" shackle, the pin diameter is 3/4 and the throat width is 1.06". Since my recovery points were tabbed from doubled up 1/4", I needed to increase this to 1". I stole
@Brian1 's idea to make 1/4" spacers to weld on to get my 1" width.
We've all heard the horror stories of winch bumpers being torn from rigs because stock bolting arrangements were used. Since I'm using only using 4 bolts in the stock locations, I went here to estimate the shear strength of my bolts:
Load Calculator | Fastenal
For 1/2" UNC grade 8 bolts, I'm coming up with an estimated shear strength of 9k lbs per bolt. So a total strength of 36k lbs. Should be plenty. I'll plate the ends of my frame horns for a little extra torsional strength, but I have no concerns about that bumper staying put.
Winch is supposed to show up on Friday! Got to wrap up my last little items so I'm ready to mount it up!