Tubular Locks: Circular Pin Tumblers and the Round Key

Two Meanings of "Tubular"

This page covers the tubular key cylinder, the round-key mechanism. The same word is also used for a common type of door lockset, and the two are unrelated.

The LIST dictionary defines a tubular lockset as "a bored lockset whose latch or bolt locking mechanism is contained in the component installed into the edge bore." Allegion's support article on tubular locks describes them as having "a center spindle assembly that extends through the center of the lock body and latch." It says they are common on interior doors and in residential applications.

The distinction from a cylindrical lockset is where the mechanism sits. The LIST dictionary defines a cylindrical lockset as a bored lockset whose mechanism "is contained in the portion installed through the cross-bore." Both are bored locksets, but:

• in a tubular lockset, the locking mechanism sits in the latch unit in the edge bore
• in a cylindrical lockset, it sits in the chassis in the large cross-bore through the door face

Neither definition requires a tubular key: "tubular" in a lockset describes the latch and chassis, not the key cylinder. The overlap in names goes back decades. A Locksmith Ledger history says McKinney introduced "a tubular lock with an adjustable backset" in the late 1930s, meaning a lockset. See cylindrical locks and latches.

How a Tubular Key Cylinder Works

U.S. Patent 1,984,202, "Key for locks," was granted December 11, 1934 and assigned to Chicago Lock Co. It describes the lock in plain terms: a cylindrical barrel, a plug that rotates in the barrel, and "an annular series of transversely split pin tumblers" between them. The parts work as a pin tumbler laid out in a circle:

• Pins. Each tumbler is split, like the key pin and driver of an ordinary pin tumbler lock. Springs push the stacks toward the face of the lock, so the splits sit off the shear line and the plug cannot turn.
• Key. The key is a hollow cylinder that slides over the end of the plug. Around its rim are semicylindrical cuts, one for each tumbler. Each cut pushes its tumbler in "to the proper extent or degree to release the plug for rotation."
• Alignment. A rib or notch on the key orients it so each cut meets the right tumbler. The patent also shows a ward on the key that passes through a groove in the barrel.
• Dead pin. The LIST dictionary defines a dead pin as "an immovable pin in a tubular lock which functions as a ward."

When every tumbler is pushed to the right depth, the splits line up at the shear line and the key can turn the plug. Mechanically, this is the same shear-line principle as any pin tumbler.

The Chicago Lock "Ace"

The name most tied to the format is Chicago Lock Company's "Ace." The company says it was founded in Chicago in 1920 and debuted the Ace tubular pin tumbler lock in 1933. A 1982 federal appeals court opinion confirms the date: "Since 1933 the Chicago Lock Company… has sold a tubular lock, marketed under the registered trademark 'Ace.'" "Ace" is a trademark, not a generic name for the key.

Period advertising shows how the lock was sold. A February 1935 Chicago Lock advertisement in Automatic Age, a coin-machine trade magazine, describes the Ace as 5/8 inch in diameter, with "seven tumblers located in a circle around plug, some mushroom or spool type." The same ads called the lock "pick proof" and "thief proof." Those were marketing claims, and they should be read as such. A 1940 advertisement shows the "Ace ROUND Key" and cites U.S. Patent 1,984,202.

Today, Chicago Lock describes the Ace as using "a circular arrangement of seven or eight pins," and notes that most of its locks carry a key code stamped on the cylinder face or the original key.

Variations

Tubular cylinders are not one size. A Locksmith Ledger overview of tubular tools lists the following, and points to key blank catalogs for size information:

• seven-pin locks
• seven-pin left-offset and right-offset locks
• eight-pin locks
• "pin-within-a-pin" designs with more tumblers
• large, standard, and small diameters

Because of these differences in pin count, offset, and diameter, the right key or blank depends on the specific lock.

Where Tubular Cylinders Are Used

The court opinion describes Ace locks as "frequently used on vending and bill changing machines and in other maximum security uses, such as burglar alarms." Chicago Lock's current materials name furniture, medical enclosures, vending machines, and kiosks. The compact, round face suits cam locks and equipment panels where a full door cylinder will not fit. See cam locks.

Key Codes and the Fanberg Case

Tubular locks are the subject of a well-known key-code case, Chicago Lock Co. v. Fanberg, 676 F.2d 400 (9th Cir. 1982). The court's account of the facts shows how a manufacturer tried to control keys:

• It sold duplicate keys only to the recorded owner of a lock.
• It kept the serial-number-to-key-code records "indefinitely and in secrecy."
• It did not sell tubular blanks to locksmiths.
• It stamped Ace keys "Do Not Duplicate."

Locksmiths servicing these locks recorded the key codes they worked out, along with the lock serial numbers. In the 1970s Victor Fanberg and his father compiled those records into a published code book. Chicago Lock sued. The Ninth Circuit reversed the lower court's injunction, holding that reverse engineering a lock you own is a proper means of discovery, so the company's trade secret claim failed.

The case is a reminder that key control rests on records, blank distribution, and policy, not on the shape of the key. See key control, restricted keyways, and key cutting.

Security in Perspective

An unusual key is not the same as a tested security rating. The LIST dictionary defines a tubular pick as "a pick designed to operate a tubular key lock," and dedicated locksmith tools for the format have long existed. A buyer who needs rated resistance should look for products tested to a published standard rather than relying on the shape of the key. See high-security locks and UL 437.

Related Topics

• Pin tumbler locks: the same shear-line principle, in a row
• Cylindrical locks and latches: not the same as a tubular key cylinder
• Cam locks
• Key control and restricted keyways
• Key cutting
• High-security locks
• UL 437
• Kwikset

Sources