Associated Locksmiths of America (ALOA) Practice Test 2025 – Your Comprehensive All-in-One Guide to Exam Excellence!

The common hole size required to drill in a door for a key-in-knob lock chassis is 2 1/8 inches. This standard size has been widely adopted in the locksmithing and door hardware industry to accommodate the typical cylinder and chassis dimensions used in most key-in-knob locks.

Using a 2 1/8-inch hole allows for proper fitting of not only the knob but also the latch mechanism associated with it. This dimension ensures that there is enough space for smooth operation and installation of the locking hardware, providing the necessary security and functionality that consumers expect from key-in-knob lock systems.

This size is standardized across numerous manufacturers, making it the go-to size for locksmiths and builders when specifying the dimensions for door preparations. Other sizes, while they may exist for specific applications or types of locks, are not as universally accepted or utilized as the 2 1/8-inch hole.