3mm  to 12mm
 
A shackle is a u-shaped, load-bearing connecting device designed to be used with a removable pin.
 
Shackles can be used in a number of different rigging and load securement applications to connect different types of lifting slings, chain, or rope to an object or to each other.
 
Shackles can be used in a variety of different applications, including:
Rigging
Towing or pulling
Lifting
Hoisting
Tie-down