Clips allow the knife to be easily accessible, while keeping it lint-free and unscathed by pocket items such as coins. Assisted opening systems have been pioneered by makers like Ken Onion with his "Speed-Safe" mechanism and Ernest Emerson's Wave system, where a hook catches the user's pocket upon removal and the blade is opened during a draw. One of the first one handed devices was the automatic spring release, also known as a switchblade. An innovation to pocketknives made possible by the thumb-stud is the replaceable blade insert developed in 1999 by Steven Overholt (U.S. Patent no. 6,574,868), originally marketed by TigerSharp Technologies and as of 2007 by Clauss. Some systems are somewhat between assisted opening and the normal thumb stud. CRKT knives designed by Harold "Kit" Carson often incorporate a "Carson Flipper", which is a small protrusion on the rear of the base of the blade such that it protrudes out the obverse side of the handle (when closed). By using an index finger and a very slight snapping of the wrist, the knife opens very quickly, appearing to operate like a spring assisted knife. When opened, the protrusion is between the base of the sharp blade and the user's index finger, preventing any accidental slipping of the hand onto the blade. Some designs feature a second "Flipper" on the opposite side of the blade, forming a small "hilt guard" such as a fixed blade knife has, which can prevent another blade from sliding up into the hilt in combat. These "flippers" are now being found on other brands of knives as well, such as Kershaw, even cheaper knives, including certain versions of Schrade's Snowblind tactical folders, and numerous others. Legal issues Pocketknives are legal to own in most countries, but may face legal restrictions on their use. While pocketknives are almost always designed as tools, they do have the potential to be considered by legal authorities as weapons. In the United States, knives are regulated by federal, state, and municipal laws. Some jurisdictions prohibit the possession or use of pocketknives that feature locking blades. Others prohibit certain blade styles perceived by law enforcement and legal authorities as optimal for offensive fighting, transforming the pocketknife from a utility tool into a deadly weapon. These might include knives with dirk, dagger (double-edge), bowie, or stiletto blades. In some jurisdictions it is illegal to conceal knives larger than a certain size