Based on zinc alloy which is extremely durable. Ideal for medium to high risk of theft, the padlocks are recommended for a wide range of security requirements. All models in this series have a par eccentric key-way, zinc alloy plated cylinder cores, and hardened steel shackle. The lock is built to resists being picked by a shim (along the sides of the shackle), and also has a unique internal mechanism that is more difficult to pick. And, because there is a metal barrier that blocks the shackle, it is also more difficult to clip with bolt cutters. Variations vary in sizes where small is 40mm Medium is 50mm and Large is 70mm. Order now from Jamboshop and have them delivered right to your doorstep.