one other thing to consider
I have a Van 2200Kgs loaded
I have 2 chains
I have 2 Bow Shackles
BOTH Bow Shackles are rated at 1.5t each
combined max for BOTH shackles is 3t - well under my loaded weight - legal...........
the individual shackle - either D or Bow does NOT have to be greater than the Mass being Towed - but combined (unless you only have 1 chain)
a 3t rated Bow Shackle is rather large, and wont fit the chains anyway............