U-locks started with Kryptonite's first model in the early 70's. Since then, the U-lock is the most recognized lock for bicycles. The U-lock design is known to thwart theives using regular tools and even sledge hammers. With a 13mm hardened steel shackle and crossbar, the KryptoLok is a step above any braided cable lock. The disc-style tumbler is very pick-resistant, and even sports a rotating weather cover for use in wet conditions. The vinyl coating keeps bike frames from getting scratched while making handling the lock easier with gloves. The KryptoLok series 2 is a Key Safe Program item for ordering duplicate keys. 2 stainless steel keys come with the lock. This lock weighs 2.85 pounds.
The anti-theft protection program that Kryptonite is so famous for is available with this lock. Please see Kryptonite's website for more details.