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.inquire and we can normally have them in a couple of days.Four (4) High Security Locks Keyed Alike w/ 8 Keys. ProSeries Padlocks are designed for Commercial/Industrial applications. The same lock with a longer shackle is also available, search 6230NKALH. Comes with a Limited Lifetime Warranty. If you order two 4-packs they will NOT necessarily be keyed the same. To buy multiple 4-packs keyed alike you need to purchase the locks via fulfilled by MERCHANT – HOW TO FIND: When you look at the listing there is a link showing the Other Sellers on Amazon. This is under the “add to cart button”. Look for the 4-pack fulfilled by Merchant LocksChocksTiedowns. If you purchase any 4-pack multiple we will automatically key all locks the same. These locks feature the BumpStop Advanced Cylinder Technology. (for explanation see more product details below). Dimensions: 2-1/2 (64mm) wide round solid steel body, each weighing 1.48 lbs. A 7/16 (11mm) diameter hardened boron alloy shackle with 1-1/8 (29 mm) inside height clearance. Chrome rustproofing provides longer life. These high security, rekeyable 5-pin cylinders with spool pins are virtually impossible to pick. And a dual ball bearing locking mechanism resists pulling and prying.