Tubular pin tumbler lock
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A tubular pin tumbler lock, also known as Ace lock, circle pin tumbler lock, or radial lock, is a variety of pin tumbler lock in which 6 to 8 pins are arranged in a circular pattern, and the corresponding key is tubular or cylindrical in shape.
Tubular pin tumbler locks are generally considered[by whom?] to be safer and more resistant to picking than standard locks, though there are several ways to open them without a key. Even though the pins are exposed, making them superficially easier to pick, they are designed so that after all pins are manipulated to their shear line, once the plug is rotated 1⁄6 to 1⁄8 around, the pins will fall into the next pin's hole, requiring re-picking to continue. As such, picking the lock without using a device to hold its pins in place once they reach their shear line requires one complete pick per pin.
Such locks can be picked by a special tubular lock pick with a minimum of effort in very little time; it is also possible to defeat them by drilling with a hole saw drill bit. Standard tubular lock drill bit sizes are 0.375 in (9.5 mm) diameter and 0.394 in (10.0 mm) diameter. To prevent drilling, many tubular locks have a middle pin made of hardened steel, or contain a ball bearing in the middle pin.
In 2004, videos circulating on the Internet demonstrated that some tubular pin tumbler locks could be easily opened with the shaft of an inexpensive ballpoint pen of matching diameter. One website revealed that the weaknesses of the tubular pin tumbler mechanism had first been described in 1992. (see Kryptonite lock).