What Are Space and Depth Keys?

Space and depth keys are a reference set of pre-cut keys used by locksmiths to manually determine the exact bitting (cut combination) of a lock when no code information or working key is available. Each key in the set represents a specific cut depth at a specific space position along the blade, allowing a locksmith to test a lock pin-by-pin and record the resulting combination.

Space and depth keys are especially useful for impressioning, lock decoding, and situations where a customer has lost all keys and no code is on file. Rather than guessing or replacing the entire lock, a locksmith can systematically work through a space and depth set to reconstruct a working key from the lock itself.

How Do Space and Depth Keys Work?

Space and depth keys work by isolating one variable at a time — either the position (space) along the key blade or the depth of a specific cut — so a locksmith can test each pin chamber individually. A "space" key has cuts at defined positions along the blade, while a "depth" key has a specific cut depth applied at a given space, based on the manufacturer's bitting specifications for that keyway.

By inserting different depth keys at a given space and checking which one allows that pin to set properly (often felt or heard as a subtle click when picking or testing), the locksmith identifies the correct depth for that position. This process is repeated across every space on the key until the full bitting combination is determined, which can then be cut onto a blank as a working key.

Key Components of a Space and Depth Key Set

A typical space and depth key set includes:

• Space keys – blanks cut only at specific space positions, used to identify pin locations

• Depth keys – blanks cut to each possible depth value at a given space, used to test pin height

• Reference chart/manual – manufacturer bitting specifications showing valid space and depth combinations for a given keyway

• Labeled key ring or case – organizes keys by keyway, space number, and depth number for fast identification during use

• Compatible keyway blanks – sets are typically keyway-specific (e.g., Schlage SC1, Kwikset KW1), so multiple sets are needed to cover different lock brands

Because these sets are precision-cut references, keeping them organized and undamaged is essential for accurate results.

What Are the Common Uses of Space and Depth Keys?

Space and depth keys are used in several locksmith scenarios, including:

• Decoding a lock when no original key or code is available

• Verifying or cross-checking a key code before cutting a replacement

• Training locksmiths in lock impressioning and manual decoding techniques

• Servicing older or undocumented locks where manufacturer code lookup isn't possible

• Confirming pin depths during rekeying when working from an unfamiliar cylinder

They're most commonly used by experienced locksmiths and locksmith training programs rather than as an everyday, high-frequency tool.

Main Characteristics of Space and Depth Keys

Space and depth key sets share several defining traits:

• Keyway-specific, matched to a single lock brand and profile

• Divided into separate space keys and depth keys for isolated testing

• Based on manufacturer bitting charts for accurate depth values

• Used for manual, pin-by-pin lock decoding rather than automated methods

• Require practice and familiarity with the specific keyway to use efficiently

These characteristics make space and depth keys a specialized, skill-based tool rather than a plug-and-play solution.

How to Use Space and Depth Keys

Using a space and depth key set to decode a lock generally follows this process:

1. Identify the keyway of the lock being decoded, and select the matching space and depth key set.

2. Start at space 1 (closest to the key's shoulder/stop) and insert depth keys one at a time, starting from the shallowest or deepest depth depending on technique preference.

3. Test each depth key by applying light rotational pressure to the plug, similar to lock picking, and noting which depth allows that pin to set properly (often felt as the plug moving slightly or a subtle give at that pin).

4. Record the correct depth for that space using the reference chart's depth numbering.

5. Move to the next space and repeat the process, testing depth keys until each pin position is decoded.

6. Compile the full bitting combination once all spaces have been tested, recording each space's depth number in sequence.

7. Cut a key blank to the recorded bitting combination using a key machine, producing a working key that matches the lock.

This process takes practice, since correctly identifying when a pin has "set" at the shear line requires a developed feel similar to lock picking. Many locksmiths first practice on clear practice locks before using space and depth keys on customer property.