How-to

The Locksmith's Guide to Restricted Keyways (Medeco, Mul-T-Lock, ASSA)

Updated 2026-05-27. Locksmith School Blog editorial team.

Defining the Restricted Keyway

In the commercial locksmithing trade, the difference between a standard keyway and a restricted keyway is the difference between a one-time service call and a long-term contract. A standard keyway, such as a Kwikset KW1 or Schlage C, uses a blank available at any hardware store. If a facility manager hands out keys to employees, those employees can walk into a Walmart and duplicate the key for a few dollars. You have no control, and neither does your client.

A restricted keyway solves this through two layers of security: physical geometry and legal patent protection. Physically, these keyways utilize complex milling, sidebars, and active elements that cannot be replicated by standard key cutting machines. Legally, the blanks are patented, and the manufacturer only sells them to locksmiths who have signed a contract and undergone a background check. This creates a "key control" system where you, the dealer, are the sole source for key duplication.

This exclusivity allows you to charge a premium for the initial hardware and a recurring fee for every additional key cut or cylinder serviced. It transforms you from a service technician into a security partner. To succeed, you must understand the mechanical differences between brands, the administrative rigor required to maintain the system, and the liability involved in holding the "bitting records" for a facility.

The Major Players and Their Architectures

While there are dozens of manufacturers, three brands dominate the North American commercial market: Medeco, Mul-T-Lock, and ASSA. Understanding the mechanical philosophy of each helps you recommend the right system for the client's risk level and budget.

Medeco

Medeco, owned by ASSA ABLOY, is arguably the most recognized name in the industry. Their classic offering, the Medeco3, utilizes a "biaxial" design. The key cuts are not just depth-based; they are also angled at 15-degree increments left or right. Inside the plug, the bottom pins must align at the correct shear line, but they must also be rotated to a specific angle to engage a sidebar fence. This dual requirement makes the lock incredibly pick-resistant and virtually impossible to duplicate without the specialized angled key blank and a machine capable of cutting those angles (U.S. Patent 6,343,508 B1, uspto.gov).

Mul-T-Lock

Mul-T-Lock, another ASSA ABLOY brand, often employs "interactive" or telescoping pin technology. In systems like the Mul-T-Lock Classic or the newer MT5+, the pins are actually two pins stacked inside one another within the chamber. The key must lift the outer pin to the shear line while simultaneously interacting with the inner pin. Some versions also incorporate a floating pin that moves laterally. This creates a massive number of theoretical key combinations, allowing for complex master key systems without cross-keying issues. Their keys typically feature a "card" cut on the side of the blade, which acts as the sidebar interface.

ASSA

ASSA (specifically the ASSA Twin V-10 or Abloy Protec lines) relies heavily on disc detainer or rotating disk mechanisms rather than traditional pins. The Abloy system, for example, uses rotating discs with angled cuts. When the correct key is inserted, the discs rotate to form a straight line, allowing the sidebar to drop. Because there are no traditional springs or pins that can be shimmed, these locks are highly resistant to bumping and picking. They are often preferred in harsh environments where dirt or corrosion might seize a standard pin-tumbler mechanism.

Establishing Your Dealership

You cannot simply order restricted blanks from a supply house. You must become an authorized dealer. This process protects the integrity of the keyway and ensures that unauthorized locksmiths cannot access the blanks.

Application and Vetting

The first step is contacting the manufacturer's regional sales representative. They will require you to submit a dealership application. This typically includes proof of business insurance, a business license, and a copy of your locksmith license. Depending on your location, the vetting process can take anywhere from a few days to several weeks. For example, if you are operating in a jurisdiction with strict oversight, you may need to provide extra documentation regarding your Locksmith Licensing in Florida (and the Two Cities That Add Their Own Rules) or similar state-level credentials.

The Buy-In

Approval usually comes with a buy-in requirement. You will likely need to purchase a "start-up kit." This kit includes the pinning kits (tumblers), the key blanks, a specialized decoding tool or caliper, and the authorization software or keyway cards. The initial investment can range from $500 to $3,000 depending on the brand and the volume of hardware you commit to buying. However, this buy-in is your barrier to entry against competitors; it is what protects your market share.

Training and Certification

Many manufacturers require you to complete a certification course before they will ship the product. Medeco, for instance, offers factory training that teaches you how to pin their cylinders correctly and how to service the sidebar mechanism. Attempting to service these locks without factory training is a recipe for liability. If you want to deepen your mechanical skills before approaching a manufacturer, a comprehensive Locksmith School Blog training overview can provide the foundational pinning and master keying knowledge necessary to handle these advanced systems.

Managing the Bitting Book and Key Records

The physical security of the lock is only half the battle. The administrative security of the key system is where you make your money and protect your liability. When you sell a restricted system, you are not just selling metal; you are selling the promise of control.

The Signature Card

Upon installation, you must issue a "Key Control Signature Card" to the client. This card lists the keyway name, the system code, and the authorized signatories. It explicitly states that keys will only be duplicated if a request is made in writing (or via email) by one of the named signatories. If an administrative assistant calls you asking for five keys, but their name is not on the card, you must refuse. If you duplicate keys without proper authorization, you invalidate the key control warranty and could be held liable for a security breach.

The Bitting Book

Never give the client the bitting list (the specific cut depths for every key). The bitting list is your property. It is the asset that ensures the client must return to you for future service. You should maintain a secure, physical logbook or an encrypted digital database of every key you issue. This record should include:

• Key Number: (e.g., A001, A002).
• Bitting: (e.g., 321453 for a standard 6-pin system).
• Issued To: The specific employee or department.
• Date Issued: For tracking purposes.

When a client loses a key, you consult your book. You can then verify that the lost key is not simply "misplaced" by checking the bitting against keys currently in circulation. If you need to remove a lost key from the system, you calculate the necessary change key and re-pin the relevant cylinder, rendering the lost key mechanically inoperative.

Servicing: Decoding and Key Generation

When a client needs additional keys, you have two methods: direct duplication and code generation. Direct duplication is straightforward if you have the original key. However, restricted keys often wear differently than standard keys due to the complex interaction of sidebars and sliders. Therefore, code generation is often the professional standard.

Visual Decoding

Most restricted systems come with a visual decoder. This is a small gauge or template that you place over the key blade. By reading the shoulder of the key against the gauge, you can determine the depth of each cut. For Medeco, you must also read the angle (left, right, or center). Once you have the code, you can input it into a code-cutting machine, such as a Framon Code Machine or an HPC 1200CM. This produces a key that is factory-fresh, within tolerances, and free from the wear patterns of an old key.

Progressive Keying

In large facilities, you will often use "progressive keying." This is a system where keys are issued in a mathematical sequence (e.g., 001, 002, 003). Key 001 might open only door 1. Key 002 might open doors 1 and 2. Key 003 might open doors 1, 2, and 3. This requires strict adherence to the manufacturer's "Maximum Adjacent Cut Specification" (MACS). If you ignore MACS, you create a "ghost key"—a key that accidentally opens a door it shouldn't. Always consult the manufacturer's technical manual before designing a progressive system to ensure the bitting increments are valid.

Master Keying Complex Systems

Master keying a restricted system is significantly more complex than a standard Schlage or Kwikset cylinder because you are dealing with multiple shear lines or sidebar interaction. You are not just matching bottom pins; you must calculate master pins that will bridge the gap between the master key cut and the change key cut while still allowing the sidebar to function.

Software Assistance

Do not attempt to hand-calculate master key systems for restricted keyways. Use industry-standard software like InstaCode or CodeSource. These programs contain the specific pinning charts and MACS rules for Medeco, Mul-T-Lock, and ASSA. You input the system parameters (e.g., a 4-level master key system with 50 change keys), and the software generates the pinning charts and the bitting lists. It will flag invalid combinations that could cause lockouts or cross-keying.

Top Pin Stacking

When pinning a high-security cylinder, be mindful of the stack height. Because you are using master pins, the total height of the pin stack might exceed the standard depth of the plug chamber. This can cause the pins to bind or "bottom out" before the cylinder is fully inserted. Most restricted systems use "shorter" springs or specific top pin heights to accommodate the extra master pins. Always measure the total stack height against the manufacturer's specification before reassembling the cylinder.

Liability and Patent Expiration

A critical aspect of selling restricted systems is understanding the lifecycle of the patent. Patents generally last 20 years from the filing date. When a patent expires, the keyway legally becomes "non-restricted." This means other manufacturers can begin selling "unrestricted" blanks that fit the keyway.

The Medeco Classic Example

The original Medeco Biaxial patent expired years ago. Today, you can buy "aftermarket" Medeco blanks from unverified sources. If you sold a client a Medeco system 25 years ago and told them it was "restricted for life," you are now in a difficult position. You must inform the client that their key control is compromised. The solution is usually a "core swap" or "re-key" to a newer, patented keyway (like Medeco3 or Mul-T-Lock MT5+).

Legal Responsibility

As a locksmith, you have a duty of care. If you fail to warn a client that their system's patent has expired, and they suffer a loss because an employee copied a key at an unauthorized kiosk, you could be named in a lawsuit. Always track the patent status of the systems you install. The Associated Locksmiths of America (ALOA) provides resources and updates regarding patent statuses and industry standards (alaoa.org).

Common Mistakes

Even experienced technicians can err when transitioning to high-security work. Avoiding these pitfalls will save you time and money.

• Ignoring the Sidebar: The most common error when servicing Medeco or ASSA locks is focusing entirely on the pin stacks and forgetting the sidebar interaction. If the lock doesn't work after you pin it, 90% of the time it is because the sidebar pins are not rotated correctly or the wrong length sidebar pin was used.
• Losing the Bitting Book: If you lose your records for a client's restricted system, you may have to re-key the entire building. This is a massive expense that will likely come out of your profit margin. Keep digital backups encrypted and physical copies in a fireproof safe.
• Mixing Manufacturers: Never try to mix pin kits from different manufacturers, even if they look similar. A Mul-T-Lock master pin might physically fit into a Medeco cylinder, but the metallurgy and tolerances are different. This will cause premature wear and eventual lock failure.
• Over-tightening Cam Screws: Restricted cylinders often have tighter tolerances than standard cylinders. If you over-tighten the set screw that holds the cam or tailpiece on the back of the cylinder, you can compress the plug slightly, causing the pins to bind. Tighten until snug, then back off a quarter-turn.

When to Call Someone Else

Restricted keyways are a specialized field. While you should aim to handle most of this work in-house, there are scenarios where calling a factory-certified specialist is the correct business decision.

• Lock Malfunction: If a high-security cylinder is failing to accept the correct key despite being correctly decoded, the internal sidebar or the interactive pins may be damaged. Attempting to force it can destroy the cylinder. Call a factory rep.
• Safe Work: Many restricted keyways are used on safe deposit boxes and safes. If you encounter a locked safe with a Medeco or ASSA lock and no key, do not drill. Safe manipulation requires specialized drilling rigs and knowledge of critical neutral points that general locksmithing does not cover.
• Access Control Integration: If a client wants to integrate their Medeco cylinders into an electromechanical access control system (like Medeco Logic or ASSA CLIQ), and you are not familiar with the programming software, sub-contract this to an access control specialist. You can learn it later, but do not experiment on a client's active security system.