This listing is for two (2) High Security Keyed Alike Padlocks w/ four keys. ProSeries Padlocks are designed for Commercial/Industrial applications. The same lock with longer shackle lengths are also available, search 6121NKALF + 6121NKALJ - or a heavier duty version of this lock is available , search 6127NKALH. If you order two 2-packs or any multiple of this lock we will automatically key them all the same. These locks feature the BumpStop Advanced Cylinder Technology. (for explanation see more product details below). DIMENSIONS: 2-1/8in (54mm) heavy steel body withstands physical attack. 1-1/8in (29mm) tall, 5/16in (8mm) diameter hardened boron alloy shackle for maximum cut resistance. Ideal for harsh outdoor conditions - exclusive Pro Series Weather Tough cover protects lock from water, ice, dirt and grime. Solid iron shackle shroud resists harsh physical attacks. The removable cylinder can be replaced or re-pinned. 5 spool pin tumbler cylinder for added pick resistance. Dual ball bearing locking mechanism resists pulling and prying. FEATURING BumpStop TECHNOLOGY - Lock bumping a surprisingly simple method of breaking in through locked doors and padlocks - is undoubtedly the newest emerging threat to personal property security. And virtually all locks in use today are particularly vulnerable to bumping. Until now. BumpStop Advanced Cylinder Technology employs an innovative, patent pending design which utilizes a unique reverse rake tapered driver pin, high performance springs and tightly machined cylinder chambers. During a bump attempt, this design prevents the transfer of force from the bump key to the pins and therefore blocks rotation of the cylinder so that the lock remains locked.