Introduction

Locks come in a variety of shapes, sizes, finishes, backsets, etc. These features were implemented to fill needs. Lock functions too were designed to fill needs. Situations exist where a door should always be locked, when it should never be locked, or when it should do X or Y. Locks with a variety of functions were and are therefore necessary to meet the needs of these situations. 

function n. a set of operating features for a particular type of lock or exit device which make it suitable for a specific application. The function is designated by a classification name or standards reference number. See ANSI or BHMA for a specific listing.

ANSI/BHMA’s Role

ANSI/BHMA standards both define and assign names and numbers (known primarily as function numbers but also as ANSI numbers or function codes) to functions. The use of function descriptions, names, and numbers is commonly associated with 2 lock types:  

1. ANSI/BHMA A156.2 (Bored & Preassembled Locks and Latches) covers bored locks, such as cylindrical knobsets and leversets.  

1. ANSI/BHMA A156.13 (Standard for Mortise Locks and Latches) covers mortise locks.  

While technically bored locks, interconnected locks and their functions are defined in their own standard, ANSI/BHMA A156.12 (Interconnected Locks & Latches); I will use the “cylindrical” nomenclature for the remainder of this article to avoid any confusion. 
Other lock types, such as deadbolts and even cylinders, have functions defined and assigned names and numbers by ANSI/BHMA standards. Mortise locks and cylindrical locksets will be the focus of this article since they carry many more functions than the aforementioned lock types. 

Standardization

Standardizing functions helps bring uniformity to our industry. All manufacturers include function names and numbers in their catalogs. If you were searching for a specific function across multiple product lines, seeing this function name and number would tell you how the lock operates regardless of the manufacturer or their product number. For example, a Schlage L9010 and a Sargent 8215 are passage function (F01) mortise locks. Here is a side by side comparison of their catalog entries, each with their function number listed: 

Unique Functions

There are multiple functions that manufacturers offer that ANSI/BHMA standards don’t define or quantify. This is especially true for mortise locks which can incorporate more features, such as a deadbolt, than cylindrical knob and leversets. For example, Schlage’s L Series mortise locks has 57 functions – less than half have a corresponding ANSI/BHMA function name or number. Fortunately, all manufacturers include drawings as well as thorough descriptions for functions that ANSI/BHMA standards don’t cover. This eliminates any guess work.  
A clear majority of the locks that we sell or service have a function name and number. With a bit of familiarity and practice, their identification will be as second nature as identifying a tool in your tool box. In this article, we’re going to discuss the most common functions, their features, and where they are generally found to help build this familiarity. I’ve included descriptions, names, and numbers from Schlage’s L (mortise) and ND (cylindrical) series locks to help illustrate each function discussed. 

Function Terminology

Before we do that, let’s take a moment to cover some terminology. When describing a lock, we need to differentiate between each side of the door. Avoid using terms like secured side. This causes confusion over interpretation. Use the terms “outside” and “inside” instead. Outside refers to the side of the door which houses the cylinder; manufacturers will sometime refer to this as the “cylinder side” of the door. Inside nearly always refers to the side of the door without a cylinder. There are functions with cylinders on both sides of the door but the manufacturer will adequately describe these functions. This is the terminology used by manufacturers and it would serve you well to not only understand it but also practice it.  

Popular Functions

Passage (F01 for mortise, F75 for cylindrical) 

The good thing about functions is that their name gives us clues to their use or operation. Passage function locks are a good example of this. They allow passage no matter which side of the door you are on. No key is required and passage locks cannot be locked. 
Passage function locks are ideal where doors are either required, such as by code, or desired to latch but not lock. Examples of their usage include common areas and on stairwell doors. They are also commonly used in conjunction with deadbolts where allowed. 

Privacy (F02, F19, or F22 for mortise, F76 for cylindrical) 

Privacy function locks allow an occupant inside of a room to lock the door from the inside via a thumbturn or push button. Turning the inside trim retracts the latch and/or deadbolt. Furthermore, there is an emergency override on the outside that a user can operate with a coin, standard screwdriver, or similar object that allows them to open the door in the event of an emergency. For mortise locks, F22 utilizes a latchbolt, no deadbolt. F02 and F19 incorporate a deadbolt. On F19 function mortise locks, the latch cannot be retracted by the outside trim when the deadbolt is thrown, on F02 function mortise locks it can (the latch and deadbolt operate independently). Privacy function locks are common on restroom doors as well as interior residential doors.  

Office/Entrance (F04 for mortise, F82 for cylindrical) 

Office/Entrance function mortise locks allow the room’s occupant to lock a door by utilizing a key and either a thumbturn or a toggle switch. Some manufacturers offer both types. For locks utilizing a toggle switch,you can only lock the door using the toggle switch. The door remains locked when turning the inside trim and using a key only retracts the latch. The toggle switch must be returned to the unlocked position to unlock the outside trim. For locks utilizing a thumbturn, the door can be locked using a key or the thumbturn. The door remains locked when turning the inside trim. The door can be unlocked by the key or by returning the thumbturn to the unlocked position.   
For cylindrical locks, F109 (Entrance Function) is very similar to F82. In fact, most people refer to them both as entrance function locks. The difference is that F109 function cylindrical locks utilize a turn-and-push button on the inside. Pushing the button will lock the door until you turn the inside trim or use the outside key to unlock it. Pushing and turning the button will lock the door indefinitely; the button must be turned back to the “push” position for it to be unlocked the next time the inside trim is turned or the key is used. Office/Entrance function locks are very popular on residences and individual commercial offices and closets. 

Storeroom (F07 for mortise, F86 for cylindrical) 

Storeroom function locks always remained locked from the outside and unlocked from the inside. You can use a key to retract the latch but that will not unlock the lock. A storeroom function lock prevents someone from inadvertently leaving the door unlocked. Storeroom function locks are popular on rooms containing sensitive information, such as server rooms, or items, such as storage rooms. Storeroom function locks are also popular with doors utilizing electric strikes. This prevents someone from unlocking the lock, relying instead on the electric strike, while still allowing for a mechanical override if necessary. 
Most manufacturers now offer storeroom function cylindrical leversets with “clutched” levers. Standard storeroom function cylindrical leversets have rigid outside levers whereas clutched levers are not; they allow movement of the outside lever without retracting the latch. This protects against destructive entry attempts to open a cylindrical leverset by forcing the outside lever trim. 

Classroom (F05 for mortise, F84 for cylindrical)

Classroom locks are very popular on, you guessed it, classrooms. The function allows only key holders, such as teachers or other school staff, to lock and unlock the outside trim of the lock. You don’t want to give students or other individuals the ability to lock the teacher out, after all! 
It’s important to note that new hardware products and lock functions are being developed by manufacturers to help protect classrooms in the event of an active shooter or similar threat. Furthermore, life safety codes related to this specific situation are actively being debated, researched, and, in some cases, revised in response. The usage of the term “classroom” is highly popular with these new functions. I cannot stress how important it is to verify the function of these locks as well as their legality in your jurisdiction before choosing to service or install them.  

Other Functions 

Passage, privacy, storeroom, entrance, and classroom functions are by far the most popular and utilized lock functions currently. You can satisfy a large majority of customer’s requests with these functions alone. There are, however, dozens more functions available. It would serve you well to familiarize yourself with different manufacturers’ offerings by reviewing their catalogs. These also serve as excellent research tools if a customer requests a lock function that you aren’t immediately familiar with.  

Universal Function Mortise Locks

BEST, Sargent, and Schlage offer multi-function/universal mortise locks. These mortise lock bodies are capable of multiple, different functions with a single lock body. Changes to the lock body, such as screws in BEST’s case as seen above, result in changes to the function. Changing of these functions can potentially require you to add, remove, or swap existing trim and/or components. For example, transforming a passage function mortise lock to a storeroom function mortise lock requires a mortise cylinder. It’s important to understand these changes when quoting to change the function of mortise locks so that you and your customer don’t incur additional costs during the job and/or potentially leave unfilled holes in the door.