Posted on: 20.08.2023 Posted by: Редакция Comments: 0

Most people will eventually replace a door knob at some point in their lives. When that time comes, you need to know what kind of door knob to buy. However, you may be wondering if all door knobs are universal or if you need to buy a specific type.

Door knobs are not universal, but there are not exponentially increasing options for what you need. You need to consider three things: the backset, the hole diameter (called cross-bore) that the door knob fits into, and whether it will be used for interior or exterior.

This article discusses the shape and functional differences of door knobs. Keep reading to learn more about the characteristic features of door knobs and how to choose the right knob for your door.

What differentiates door knobs?

Door knobs are differentiated by their compatibility with different backsets, cross-bores, and installation locations. Additionally, door knobs for exterior have different functions and features compared to knobs for the interior.

The backset length affects the choice of door knob

The backset is the distance from the edge of the door to the center of the hole where the knob goes. Most door knobs have a backset of either 2 ⅜ inches or 2 ¾ inches (6.03 cm or 5.08 cm). This means different things depending on the situation.

If you have an existing hole in the door (which is likely if you are replacing a door knob), you need to measure the backset to get a suitable replacement. If the door does not yet have a hole, you need to know the backset of the door knob you want to install so you know the right spot to use your hole saw.

You can buy a set of these or just one in a Dewalt Door Lock Installation Kit (available on like this one. This installation kit is highly rated and compatible with doors of different thicknesses.

The wrong backset length can cause problems with the latch assembly moving when you turn the knob. Using a knob that is not compatible with the backset length means that the latch assembly will either be too long to lock the door or too short to reach the door knob.

Cross-bore diameter affects door knob compatibility

The cross-bore typically measures 2 ⅛ inches (5.08 cm) in diameter, although there are some exceptions. Like the backset, you either need to know the diameter of the hole in your door, or you should know the size of cross-bore your knob requires before cutting your new door.

In some cases, you may come across a larger cross-bore that requires a wider door knob and a wider rosette. The rosette is the round metal plate that goes around the door knob and covers the mechanics of the door knob.

Interior vs. exterior door knobs

Where your door knob goes is just as important as its measurements. It’s important to understand that different door functions require different knobs.

Interior door knobs are lighter

Typically, a light door knob is used, an interior knob is usually smaller and lighter than an exterior knob. They are designed to keep interior doors closed and do not provide serious security. Since interior doors are often hollow core doors, they have less weight. Interior door knobs do not need to work very hard to keep them closed.

Additionally, most interior knobs do not have a locking mechanism. They can be divided into three categories:

  • Passage knobs: These knobs cannot be locked and are usually found on cabinet doors and the like.
  • Dummy knobs: Serve an aesthetic purpose and do not turn a mechanism (they don’t turn at all).
  • Privacy knobs: These knobs have a lock without a key – instead, there is only a hole on the other side of the knob. These are usually found on bathroom and bedroom doors.

The lock on a privacy knob is not very secure, so you would not want to use this type on an exterior door. Rather, they provide a lower level of security that preserves privacy in a locked space (as the name suggests).

Exterior door knobs focus on security

While we usually think of door knobs as a tool for opening doors, the main function of an exterior door knob is to securely close the door. They have key locks and a more sturdy construction than their interior counterparts. Although they are not impenetrable, they are more robust than interior knobs.

Keyed entry knobs provide additional security

Most of us grew up with a key-entry exterior door knob at the front door. The lock on this knob is more difficult to pick than a privacy knob, which can be easily released with a bobby pin. You can still pick a key-entry knob with a bobby pin, but it is more complicated than a privacy knob.

Most of the time, keyed knobs come with deadbolts, similar to this Kwikset Entry Combo Set (available on This knob set is relatively inexpensive and comes with hardware for the interior and exterior sides of your door.

While exterior knobs provide better security than an interior passage knob, they are usually much more effective when paired with a deadbolt installed on top.

Keyless entry knobs work without physical keys

Keyless knobs have been gaining popularity lately. They are usually operated with battery power, and although they usually have a key and keyhole, their main function is to work without that physical metal key. Keyless knobs can have a numeric keypad where you enter a 4-digit code to open or close the lock, or there may be a key fob or some other method.

Think of a hotel: When you check-in, you receive an electronic key in credit card size. Keyless entry knobs work on a similar principle and allow you to open the lock without a physical metal key.

Some smart homes offer lock operation through a smartphone app, which follows the same principle. These smart locks provide a way to open your door without a key. If you are a person who frequently loses keys, this can provide great convenience and save the cost of a locksmith or a visit from a window replacement service.

Even if you don’t have a fully equipped smart home, you can buy a standalone lock like this Level Bolt Smart Lock on This lock is easy to set up and works with Bluetooth technology.

Older door knobs can make replacement difficult

If your door is approaching antique status, you may be ready to find a more modern and secure door knob. In this case, you may find that you need to drill new holes. In some cases, you may even need to replace the door completely.

Older knobs may have a much narrower spindle. In other words, the spindle is the metal piece that the knob rotates to activate the latch. In this case, the cross-bore may be much too small for the new knob. You may also encounter a different backset than one of the common sizes.

The first issue can be addressed with a hole saw. You simply use the saw to cut a larger hole in the door. The second issue means you will need to move the hole either to the left or right. Keep in mind that you may still have the old hole in the door after completing this process.


While door knobs are not universal, they are fairly standardized depending on your specific needs. Knowing the backset will allow you to purchase the right replacement or drill the cross-bore in the right spot on the door. Determining whether you need interior or exterior knobs further narrows down the field to choose from.

Know your measurements before starting to cut your door. “Measure twice, cut once” is a cliché because it is sound advice.


  • Lot Questions: What is a cross-bore on a door?
  • Bob Villa: Solved! What Is a Keyless Entry Door Lock, and Is It a Secure Option for Home?
  • Chatfield Court: Replacing Old Door Knobs and Hinges
  • Compact Appliances: How to Buy a Door Knob (It’s More Complicated Than You Might Think)
  • eHow: How to Measure for the Correct Door Knob Size
  • House of Antique Hardware: Antique Door Knobs
  • Lowes: Determine Your Door’s Backset
  • SF Gate: How to Measure for the Right Door Knob Size
  • CDSE: Glossary – Lesson: Lock and Key Systems
  • Art of Lockpicking: The Beginner’s Guide to Bobby Pin Lockpicking

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