Tubular Keys

Tubular keys are a distinct category of key identified by their hollow, cylindrical shaft and the radial arrangement of cuts around the tip, which engage pin tumblers positioned in a circular pattern inside the corresponding lock cylinder. Unlike flat, blade-style keys that move through a horizontal keyway, a tubular key slides straight into the face of a tubular lock and rotates the entire plug by pressing all pins simultaneously — a mechanism that requires precise tolerances and, for that reason, rewards careful professional handling. Common alternative names include barrel keys, cylinder keys, chicago keys, and round keys, each reflecting a different trade tradition or regional preference, though all refer to the same fundamental design.

Because tubular locks appear across a wide range of everyday equipment — from vending machines and bicycle U-locks to laptop security cables and coin-operated laundry units — tubular key duplication and replacement come up regularly in both residential and commercial locksmith work. Despite their compact appearance, tubular lock and key systems involve engineering tolerances that are tighter than many standard pin-tumbler locks, which means that improperly cut tubular key blanks or worn originals can cause frustrating operational failures. This entry covers what tubular keys are, where they appear, the most common service problems associated with them, and the circumstances under which calling a professional is the practical choice.

What Is a Tubular Key

Plain Language Definition

A tubular key is a key whose blade is a hollow metal tube rather than a flat shank. The tip of the tube is milled with a series of cuts — typically six, seven, or eight — arranged in a ring around the circumference. Each cut corresponds to a spring-loaded pin inside the tubular lock cylinder. When the key is inserted and rotated, all cuts engage their respective pins at the same moment, aligning the shear line around the full circle of the plug and allowing it to turn. This simultaneous, radial engagement is what sets tubular keys apart mechanically from conventional keys, where cuts engage pins in a linear sequence along a flat blade.

The shaft diameter and the number of cuts are the two primary specifications that define tubular key blanks. The most widely encountered shaft diameter in North American equipment is 7 mm, though 6.35 mm and other metric sizes exist in imported goods. Cut count — six, seven, or eight pins — determines which blank series applies. Because cut depth and angular spacing must match the lock exactly, tubular key duplication requires either a dedicated tubular key cutting machine or a skilled technician with manual filing equipment. Standard key-cutting machines found at hardware counters cannot process tubular key blanks, which is why many owners find themselves unable to get a spare cut at a general retail location.

The name “chicago key” has historical roots in the vending and amusement machine industries, where tubular locks were standardized across coin-operated equipment manufactured in the Chicago area during the mid-twentieth century. That regional legacy explains why operators and technicians in those industries still prefer the chicago keys label, even though the hardware itself is identical to what a cyclist might call a round key for a U-lock.

Where It Is Used

Tubular locks and tubular keys appear in a broader range of applications than most people expect. The following categories account for the majority of tubular lock and key encounters in everyday life and commercial environments.

Vending and coin-operated equipment. Vending machines for beverages, snacks, and laundry tokens have used tubular locks as the primary entry-door lock on their cash and product compartments for decades. The compact size of a tubular cylinder fits neatly into the limited panel space of a vending cabinet, and the simultaneous pin engagement makes picking slightly more involved for casual intruders. Operators routinely carry spare tubular keys and rely on locksmith work when a key is lost or a cylinder wears out.

Bicycle U-locks. Many mid-range bicycle U-locks use a tubular cylinder because the round format fits the cylindrical body of the lock shackle housing efficiently. Cyclists who lose their only tubular key face a straightforward choice: professional tubular key duplication from the manufacturer’s code card (if retained) or cutting the lock off and replacing it.

Laptop and equipment security cables. Kensington-style laptop locks and cable locks for monitors, projectors, and other portable equipment almost universally use a tubular cylinder. The slim profile of the tubular lock cylinder allows it to fit into the standardized security slot found on laptops and audiovisual gear without adding significant bulk.

Tubular cam locks in furniture and cabinetry. Filing cabinets, display cases, electrical panels, and office furniture sometimes use tubular cam locks rather than the more common pin-tumbler cam lock. In these settings, tubular keys provide a keying option that looks inconspicuous and operates smoothly under light daily use.

Arcade and amusement machines. Arcade game cabinets, prize redemption machines, and amusement rides have long relied on tubular locks for coin box access and control panel security, continuing the chicago keys tradition in the amusement industry.

Medical and laboratory equipment. Certain controlled-access drawers, medication carts, and instrument storage units use tubular cylinders because the round key format is easy to handle with gloved hands and the compact cylinder integrates well into custom enclosures.

Security and Service Considerations

Common Problems

Tubular keys and tubular locks share a set of recurring problems that technicians encounter in the field. Understanding these issues helps owners make informed decisions about repair versus replacement.

Lost or single-copy key situations. Many tubular lock and key combinations ship with only one or two keys, and owners rarely make spares before the originals are lost. Because tubular key duplication cannot be performed on standard retail equipment, losing the only copy creates an immediate access problem. A technician can decode the lock by disassembling the cylinder or by using a tubular lock decoder — a calibrated gauge that reads pin depth positions through the keyway — and then produce a correctly cut replacement from appropriate tubular key blanks.

Worn keys causing intermittent operation. High-cycle applications such as daily-use vending machines wear the cut profiles of tubular keys over time. As the cuts shallow out, the key fails to fully depress the pins to the shear line, causing the plug to bind or require excessive force to turn. Owners sometimes compensate by applying more rotational pressure, which accelerates wear on both the key and the pin chambers. Replacing the tubular key — rather than the lock — at the first sign of stiffness typically avoids the larger cost of cylinder replacement.

Key broken inside the cylinder. The hollow shaft of a tubular key is structurally thinner than a comparable flat key blade, and forceful operation on a binding cylinder can fracture the tip inside the lock. Extraction of a broken tubular key tip requires specialized picks and controlled rotation techniques; forcing the remnant out risks damaging the pin chambers and necessitating a full cylinder replacement.

Cylinder wear and pin failure. In high-traffic vending and coin-operated environments, the pin chambers of a tubular cylinder accumulate debris, corrode from humidity, and experience spring fatigue. When individual pins begin sticking, a correctly cut tubular key will still fail to operate the lock. In these cases, cylinder replacement is the appropriate repair, and the replacement cylinder should be re-keyed to match any remaining tubular key copies the operator holds.

Tubular key blanks that do not match the lock. Not all tubular key blanks are interchangeable. Using a blank with the wrong shaft diameter, cut count, or angular spacing produces a key that may partially insert but will not correctly align the pins. Improper blanks can also damage the pin chambers if forced. Correct blank selection requires knowing the lock manufacturer, model, and keyway series — information a professional technician can determine from the lock itself or from manufacturer documentation.

Security vulnerabilities from standardized keying. A notable limitation of tubular locks in commercial settings is that many equipment manufacturers ship units with factory-standard tubular keys shared across large production runs. In the vending industry, for example, a technician carrying a common factory key blank may be able to operate a significant share of machines from multiple operators. Owners of high-value vending equipment should discuss re-keying or upgrading to higher-security tubular cylinders with a locksmith familiar with commercial equipment, particularly in locations with public access.

Related Locksmith Work

Several categories of professional locksmith work center specifically on tubular keys and tubular lock cylinders.

Tubular key duplication and cutting. Professional tubular key cutting service uses a dedicated machine that clamps a blank and a reference key (or a decoder reading) and mills the cuts to exact depth around the circumference of the blank. The precision required means that quality control — testing the cut key in the actual lock before leaving the site — is standard practice for responsible technicians. A freshly cut tubular key that binds or spins freely indicates a calibration issue with the cutting equipment or an incorrect blank, both of which should be corrected before the job is closed.

Tubular lock decoding and key origination. When no original tubular key exists, a technician can originate a new key from the lock itself. Decoding may be done mechanically with a tubular decoder gauge, or by controlled disassembly of the cylinder to measure each pin’s height. The decoded measurements are transferred to the cutting machine, and a working tubular key is cut from the correct blank. This service is common in vending machine management, estate situations, and equipment acquisitions where documentation of the original keying is unavailable.

Broken key extraction. Removing a fractured tubular key tip from a cylinder is a delicate procedure that requires fine extraction hooks and, in some cases, partial disassembly of the lock body. A technician who performs this work carefully preserves the cylinder and its pin chambers, allowing a replacement tubular key to be cut and used without further expense. Improper extraction attempts with improvised tools frequently result in cylinder damage that elevates the cost to a full replacement.

Cylinder replacement and re-keying. When a tubular cylinder is worn beyond reliable service or when security requires a keying change, cylinder replacement is performed. Re-keying a tubular lock to an existing tubular key — or to a new key cut for the purpose — requires access to the correct replacement cylinder in the appropriate diameter, cut count, and cam configuration for the equipment. Professional technicians who work regularly with vending, amusement, or office equipment maintain inventory of common tubular cylinder specifications.

Master keying tubular systems. Some operators who manage large fleets of coin-operated equipment use master-keyed tubular systems, where one master tubular key operates all cylinders on a property while individual change keys operate only specific machines. Setting up a master keyed tubular system requires careful pin-stack engineering and high-quality cylinders; the work is specialized and benefits from a technician with documented experience in commercial tubular keying systems.

Security assessments for tubular lock applications. Owners concerned about the baseline vulnerability of standardized factory tubular keys on their equipment can request a security review. A qualified technician will evaluate whether existing tubular cylinders are keyed to common factory codes, recommend re-keying or cylinder upgrades where warranted, and document the keying system for the owner’s records. This type of preventive locksmith work is particularly relevant for unattended vending routes and self-service laundry facilities.

When to Call a Locksmith

Call a professional for any tubular key or tubular lock situation where a hardware store cannot help — specifically: lost tubular keys with no spare, a broken tubular key tip lodged in a cylinder, a cylinder that binds despite a visually intact key, the need for tubular key duplication without an original to copy, or any situation requiring cylinder replacement or re-keying on commercial equipment. Attempting to pick, drill, or force a tubular lock without proper tools frequently results in cylinder damage that makes professional recovery more expensive. A trained technician with dedicated tubular key cutting equipment and the correct tubular key blanks can resolve most tubular lock and key problems on-site during a single visit. Low Rate Locksmith provides mobile locksmith work for tubular key cutting, origination, extraction, and cylinder service across the US and Canada, available around the clock at (833) 439-8636. Travel is free within the service area, and pricing is provided up front before any work begins.

Related reading: Dimple Keys and Cam Locks.

Related from Low Rate Locksmith: Residential Tubular Keys, Residential Tubular Pin Tumbler Lock, Set Screw, Tubular Key Cutter, Barrel Keys, Door Lock Cylinder.