Master Key System Guide

See the Key Levels

What Is a Master Key System?

A master key system is a keying plan with two or more levels of keys. Each person carries a key that opens only the doors they need, while a few higher-level keys open whole groups of doors. Managers get access without a ring of keys, and you can rekey one area without rekeying the whole building.

Levels of a Master Key System

Each level of keys opens everything below it. Pick a system size to see how the keys fit together. The symbols are the codes stamped on each key and cylinder.

Levels of a master key system
Level	Key	Abbreviation	Example symbol	What it opens
Level 4	Great Grand Master Key	GGMK	GGMK-A	Every lock in the system, across all buildings or areas.
Level 3	Grand Master Key	GMK	A	Every lock under its master key groups, for example one building.
Level 2	Master Key	MK	AA	A group of change key locks, for example one floor or department.
Level 1	Change Key	CK	AA1	One lock, or a group of keyed alike locks.

For security, PDQ does not recommend systems with more than four levels. Every extra level adds master pins, which raises the chance of keys opening locks they shouldn't.

Four Ways to Key a Project

Every project uses one or more of these. Your PDQ rep can combine them on the same job.

Each lock has its own key

Default

Keyed Different KD

Every lock has its own key. PDQ locks ship keyed different unless you specify otherwise.

Best forPrivate offices, storage rooms and any door that shouldn't share a key.

One key opens every lock in the group

Simple

Keyed Alike KA

A group of locks opens with one key.

Best forA small group of doors, like every door in one suite or a building's exterior doors.

Master key on top, a change key for each lock

Most common

Master Keyed MK

Each lock keeps its own change key, and a master key opens the whole group. Add levels as the building grows.

Best forSchools, offices, healthcare and multifamily buildings.

Temporary key works until the owner's key is used

New construction

Construction Master Keyed CMK

Contractors use one temporary key during construction. Once the owner's permanent key is used in each lock, the construction key stops working, with no cylinder swap.

Best forNew buildings where the contractor needs access before the owner moves in.

Choose Your Key Control

The keyway decides who can copy your keys. Choose it before the levels, because changing keyways later means replacing every cylinder.

Key control level	PDQ keyways	Who can copy keys	Best for
Open (standard)	Schlage C (default) and other standard keyways	Any locksmith, hardware store or home center	Doors where quick, easy key copies matter more than control
Exclusive	PDQ1, PDQ2	Hard to copy. The key blanks are very hard to find in the marketplace	Cutting down on unauthorized copies without registration paperwork
Restricted	TA, PDQ3	Only PDQ, with a letter of authorization from the owner. Every key is registered and no blanks are sold	Facilities that need to stop copies made at lock shops, hardware stores and home centers
High Security Cylinder	PDQ proprietary high security keyway with sidebar. Conventional cylinders plus SFIC and LFIC cores	Only PDQ. Keys ship cut from the factory and no key blanks are sold	Server rooms, records storage, pharmacies and exterior entries that need drill and pick resistance as well as key control
Patented (VAULT)	VAULT SFIC keyways	Only PDQ, with a letter of authorization. The design is patent protected through 2044	Campuses that want top key control and a phased upgrade. VAULT keys also operate many standard SFIC cores (check availability)

Conventional or Interchangeable Core?

The cylinder format decides how fast you can rekey when a key goes missing.

Conventional cylinder

How it's rekeyed: A locksmith removes and repins the cylinder. Some breakdown of the lock is needed.
Works with: Key-in-lever, mortise and rim cylinders on PDQ hardware. Most come as 6-pin cylinders keyed to 5 pins.

The standard choice when the owner already has a locksmith and rekeying is rare.

PDQ small format interchangeable core (SFIC)

Small format IC (SFIC)

How it's rekeyed: Pull the core with a control key and drop in a new one. No tools and no locksmith visit.
Works with: Any SFIC housing, including other brands' SFIC hardware, in Best-compatible keyways.

PDQ SFIC cores add a sidebar for extra security. This is the format VAULT uses.

PDQ large format interchangeable core (LFIC)

Large format IC (LFIC)

How it's rekeyed: Same control-key swap as SFIC.
Works with: PDQ LFIC uses the Schlage LFIC format. Large format cores usually only fit one manufacturer's hardware.

Available in high security. LFIC cores can't be ordered zero bitted.

Keying Terms in Plain English

The abbreviations you'll see on hardware schedules, keying forms and quotes.

Search terms

Bitting: The numbers that describe the cuts on a key. Two keys with the same bitting and keyway open the same locks.
Bitting list: The record of every key's cuts in a master key system. PDQ releases it to a distributor only with written authorization from the building owner.
Change key (CK): The lowest key in a system. It opens one lock, or a group of locks that are keyed alike.
Combinate: To set a lock, cylinder or key to a specific combination.
Concealed key control (CKC): The key symbol is stamped where occupants can't see it, such as the back of the cylinder or the side of a core. More secure than visual key control.
Construction core: A temporary core used while a building is under construction, then swapped for the permanent core. PDQ offers returnable and disposable construction cores.
Construction master key (CMK): A temporary key the contractor uses during construction. It stops working for good once a permanent key is used in each lock, with no need to remove the cylinders.
Control key: The special key that removes and installs interchangeable cores. Keep very few of these.
Core: The removable part of an interchangeable cylinder that holds the plug, pins and springs. It has a figure-eight shape.
Cross keying: Setting up one key to open a lock outside its normal group. PDQ recommends avoiding it, because it weakens the system.
Grand master key (GMK): A key that opens all the locks under two or more master key groups, such as a whole building.
Great grand master key (GGMK): The top key in a four-level system. It opens every lock in the system.
Interchangeable core (IC): A cylinder core that can be removed and replaced with a control key, so locks can be rekeyed in seconds without removing the lock.
Key symbol: The code stamped on a key or cylinder that shows where it sits in the system. For example, AA1 is change key 1 under master key AA and grand master key A.
Keyed alike (KA): Two or more locks set to open with the same key.
Keyed different (KD): Every lock has its own key. This is how locks ship unless you specify otherwise.
Keying schedule: The detailed list of how every cylinder in a project is keyed, plus key quantities, stamping and shipping instructions.
Keyway: The shaped opening in a cylinder that only accepts a key blank of the matching profile. The keyway sets how hard keys are to copy.
Large format interchangeable core (LFIC): An interchangeable core with a larger body that usually fits only one manufacturer's hardware. PDQ LFIC uses the Schlage format.
Letter of authorization: A letter on the building owner's letterhead that lets a distributor order restricted keys, blanks, cylinders or the bitting list.
Master key (MK): A key that opens a group of change key locks, such as one floor or department.
Master key system: Any keying arrangement with two or more levels, so some keys open more locks than others.
Master pin: An extra pin inside a cylinder that lets more than one key operate it. More levels mean more master pins.
Restricted keyway: A keyway PDQ sells only to authorized users. Keys and cylinders need a letter of authorization.
Selective master key: A key for a specific job, such as housekeeping or engineering, that opens a chosen set of locks across the system.
Sidebar: A second locking feature inside PDQ cylinders that the key must also line up, for added security.
Small format interchangeable core (SFIC): An interchangeable core with a standard small figure-eight shape that fits any brand's SFIC housing.
Visual key control (VKC): The key symbol is stamped on the face of the cylinder and on the key, so keys and locks are easy to match. Convenient, but less secure.
Zero bitted: A cylinder set to the manufacturer's "0" combination, usually so it can be keyed later.

Plan It Before You Order

A keying plan is much easier to get right on paper than to fix after the cylinders ship. Use PDQ's keying forms to lay out the levels and list every door, then send them to your PDQ rep with the hardware order.

Download PDQ's Keying Forms

Includes the Master Key System Summary Form, a Keying System Worksheet and the Keying Schedule Form. Print them or fill them out, then send them with your order.

Download Keying Forms (PDF)

PDQ keying technician pinning cylinders at a keying workstation

From Floor Plan to Keys in Hand

List every opening. Start with the exterior doors and work inward. Group openings by building, floor or department.
Choose key control and a cylinder format. Decide who should be able to copy keys, and whether you want interchangeable cores for fast rekeying.
Set the number of levels. Use as few as the building needs. PDQ recommends no more than four.
Decide who carries what. Key to the security plan, not to individual people. Limit top master keys and control keys to a few, and avoid cross keying.
Fill out PDQ's keying forms and send them to your PDQ rep with the hardware order.

Find Your Local Rep Contact PDQ

Master Keying FAQs

What is a master key system?

A master key system is a keying plan with two or more levels of keys. Each person carries a key that opens only the doors they need, while a few higher-level keys open whole groups of doors. It gives managers access without a ring of keys, and lets you rekey one area without rekeying the whole building.

How many levels can a master key system have?

Most systems have two to four levels: change keys, master keys, grand master keys and, on the largest systems, a great grand master key. PDQ does not recommend more than four levels. Each added level needs more master pins in every cylinder, which raises the chance of a key opening a lock it shouldn't.

What is the difference between keyed alike and keyed different?

Keyed different (KD) means every lock has its own key, and it's how PDQ locks ship unless you specify otherwise. Keyed alike (KA) means a group of locks opens with the same key. A master key system combines both ideas: locks keep their own change keys, and master keys open the group.

What is a keying schedule?

A keying schedule lists how every cylinder on a project is keyed: the door number, key symbol, hand, quantities, stamping and shipping instructions. PDQ's Keying Schedule Form is used together with the Master Key System Summary Form. Both are in the keying forms PDF on this page.

What is a construction master key, and how is it voided?

A construction master key (CMK) lets contractors open every PDQ cylinder while the building is under construction. PDQ uses the lost ball method: when the owner's permanent key is used in a cylinder, the construction key stops working in it, with no need to remove the cylinder. PDQ packs and ships the permanent master and change keys separately, so construction orders need the names and addresses of the people who should receive each set.

What is the difference between SFIC and LFIC?

Both are interchangeable cores that you remove and replace with a control key, so you can rekey a door in seconds. A small format interchangeable core (SFIC) has a standard size that fits any brand's SFIC housing. A large format interchangeable core (LFIC) is larger and usually fits only one manufacturer's hardware. PDQ's LFIC uses the Schlage format.

How do I get extra keys or a bitting list for a restricted keyway?

For restricted keyways, PDQ needs a letter of authorization on the building owner's letterhead before it will release the bitting list, cut keys, master level keys, key blanks or cylinders to a distributor. No letter is needed when the items ship directly to the end user.

How do I order a master keyed project from PDQ?

Order through your local PDQ rep or an authorized PDQ distributor. Fill out the Master Key System Summary Form and the Keying Schedule Form, and send them with your hardware order. If you're adding to an existing PDQ system, include the original PDQ sales order number so the new cylinders match.

More on PDQ keying: Key Systems and Cores · VAULT Patented Keying System · Interchangeable Cores and Key Control · Master Keying: The Key to Efficient Access Control

Need Help Planning Your Key System?

PDQ's keying team can tailor a system to your building. Tell us about your project and we'll connect you with your local rep.