Lock Industry Standards and Training (LIST) Council describes levels of keying as the divisions of a master key system into hierarchies of access, as shown in the following tables.
Note: the standard key coding system has been expanded to include key symbols for systems of more than four levels of keying.
TWO LEVEL SYSTEM |
| LEVEL OF KEYING |
KEY NAME |
ABB. |
KEY SYMBOL |
| Level II |
master key |
MK |
AA |
| Level I |
change key |
CK |
1AA, 2AA, etc. |
THREE LEVEL SYSTEM |
| LEVEL OF KEYING |
KEY NAME |
ABB. |
KEY SYMBOL |
| Level III |
grand master key |
GMK |
A |
| Level II |
master key |
MK |
AA, AB, etc. |
| Level I |
change key |
CK |
AA1, AA2, etc. |
FOUR LEVEL SYSTEM |
| LEVEL OF KEYING |
KEY NAME |
ABB. |
KEY SYMBOL |
| Level IV |
great grand master key |
GGMK |
GGMK |
| Level III |
grand master key |
GMK |
A, B, etc. |
| Level II |
master key |
MK |
AA, AB, etc. |
| Level I |
change key |
CK |
AA1, AA2, etc. |
FIVE LEVEL SYSTEM |
| LEVEL OF KEYING |
KEY NAME |
ABB. |
KEY SYMBOL |
| Level V |
great great grand master key |
GGGMK |
GGGMK |
| Level IV |
great grand master key |
GGMK |
A, B, etc. |
| Level III |
grand master key |
GMK |
AA, AB, etc. |
| Level II |
master key |
MK |
AAA, AAB, etc. |
| Level I |
change key |
CK |
AAA1, AAA2, etc. |
SIX LEVEL SYSTEM |
| LEVEL OF KEYING |
KEY NAME |
ABB. |
KEY SYMBOL |
| Level VI |
great great grand master key |
GGGMK |
GGGMK |
| Level V |
great grand master key |
GGMK |
A, B, etc. |
| Level IV |
grand master key |
GMK |
AA, AB, etc. |
| Level III |
master key |
MK |
AAA, AAB, etc. |
| Level II |
sub-master key |
SMK |
AAAA, AAAB, etc. |
| Level I |
change key |
CK |
AAAA1, AAAA2, etc. |
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