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The key pins (red) and driver pins (blue) are pushed towards the front of the lock, preventing the plug (yellow) from rotating. The tubular key has several half-cylinder indentations which align with the pins.

The protrusion on top of the key fits into the rectangular recess in the lock, causing the indentations to properly align with the pins. When the key is inserted, the gaps between the key pins (red) and driver pins (blue) align with the shear plane separating the plug (yellow) from the outer casing (green).

With the pins correctly aligned, the lock may turn.

A tubular pin tumbler lock, also known as Ace lock or "axial pin tumbler lock" or "radial lock", is a variety of pin tumbler lock in which 6-8 pins are arranged in a circular pattern, and the corresponding key is tubular or cylindrical in shape.

J.A. Blake is credited with patenting the first tubular lock in 1833. Walter R. Schlage continued the development of the tubular lock. He was awarded 11 patents, and his improvements made the tubular lock what it is today.

Tubular locks are commonly seen on bicycle locks, computer locks, and a variety of coin-operated devices such as vending machines and coin-operated washing machines.

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Tubular pin tumbler locks are generally considered 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 such 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 over a dozen complete picks to unlock and relock.

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 special “hole saw” drill bit. Standard tubular lock drill bit sizes are .375" (9.53 mm) diameter and .394" (10 mm) diameter.[1] 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 (e.g. BIC brand) of matching diameter. Trade website BikeBiz.com revealed that the weaknesses of the tubular pin tumbler mechanism had first been described in 1992 by UK journalist John Stuart Clark (see Kryptonite lock).