Pewag offers three sizes of security chain to fit virtually any application. Most popular is their new 1/2" (12mm) Square Security Chain, which has a new electro-galvanized finish and is considered by many to be the biggest and baddest of them all.One step down from there is Pewag's Original 3/8" (10mm) Security Chain, which is a nice compromise on size without sacrificing hardness or toughness. The two chains are virtually identical, just one is bigger than the other. Finally, Pewag offers their Compact 9/32" (7mm) Security Chain, which is just like the bigger sizes except in a compact form (it still has a hardness of 62 HRC Min.). We recommend either of the bigger size for commercial or high dollar applications, and the smaller chain is great for urban commuters looking to secure a bicycle, scooter, etc. All sizes feature a square link shape that does not allow bolt cutters to get a proper bite, which in turn prevents them from cutting the chain.