Glossary Terms - M


Metal oxide varistors – a device used at the load to reduce electronic kickback and electrical noise.


Maximum adjacent cut specification used in pinning cylinders.

Magnetic Stripe Card

An access card with a band of magnetic material that must be inserted into a magnetic stripe reader in order to gain access or complete a transaction. Often used for credit and debit cards, magnetic stripe technology is less secure than today’s credential technologies.

Main Arm

The part of a double lever arm that connects directly to the pinion of the closer.

Maintained Contact

Switches which will remain in the same position until being manually moved to another position. Similar to a light switch.

Manual Flushbolt

A mortise bolt installed near the top and bottom of the inactive leaf of a pair of doors in which the bolts are manually extended or retracted into or out of the header or sill by means of a lever.

Master Key

A key that operates all of the master keyed cylinders in a group, with each cylinder usually having its own change key.

Master Keyed

A group of cylinders combinated in such a way that all may be operated by their own change key and a MASTER KEY.

Master Keyed System

(LEVEl 2 SYSTEM) – A key system that has two or more levels of keying.

Master Keying

Preparation of a cylinder to operate with keys of differen tlevels of access.

Master Ring Cylinder

A cylinder which offers a wider range of keying.

Meeting Stile

The vertical edge of a door, when used in a pair, that is adjacent to the other door of the same pair.

Milli Amp

One thousandth (1/1000) of an Ampere.

Mobile Access

The use of a mobile device, such as a smartphone, tablet or wearable, to gain access to secured doors, gates, networks, services and more.

Mogul Cylinder

A very large pin tumbler cylinder whose pins, springs, key, etc. are also proportionally increased in size. It is typically used in prisonl ocks.

Momentary Contact

Switch contacts that remain in one position only while being acted upon. Similar to a door bell push button.

Mortar Box

Used to protect the area and/or wiring behind electrical components. Located in the same frame.

Mortise Lock

A lock that is designed to install into a mortised pocked in the door edge, rather than being applied to the doors surface. The lock trim then bolts into or through the lock case and door face.

Mortise Preparation

Reinforcing, blocking, drilling and/or tapping for hardware that requires such a preparation in a door or frame.


The method by which the closer is attached to the door and frame.


A fixed or removable vertical member that divides a door opening and provides a latch surface for a pair of rim exit devices.


A tool used to determine voltage, amerage, and resistance in a circuit.

Multiple Backcheck Location Valve

valve which can change where backcheck occurs.

Multiplex Key System

A series of different key sections which may be used to expand a master key system by repeating bittings on additional key sections. The keys of one key section will not enter the keyway of another key section.

Multi-Point Hold Open

Infinite hold-open points from zero up to a maximum degree of the opening.

Multi-Section Key Blank

A key section which enters more than one, but not all keyways in a multiplex key system.