Mammoth Sold Secure Gold Approved 12mm x 1.8m Square Chain With Shackle Lock - LOCM003
If you are looking for the ultimate security then you must look to Thatcham for an approved device. This Mammoth chain lock uses 12mm square link Cro-Mo steel which is formed into narrow links that provide exceptional strength while greatly reducing any leverage a potential thief may apply. 
No-nonsense security
Super heavy-duty lock
Thatcham Approved chain
Sold Secure “Gold” equivalent
12mm Cro-Mo square steel chain
1.8m chain length - Also available in 1.2m (LOCM007)
Hardened steel lock body with double bearing lock mechanism
Reinforced cylinder plates resist drilling and picking
11mm hardened Cro-Mo steel shackle lock
Protective fabric sleeve