All About GM General Motors Lettered Square and Round Key Blanks
General Motors began using the older style lettered square and round key blanks back in 1968, and they continued to use the blanks into the 2000's. I believe GM stopped manufacturing cars that used the lettered keys in 2002. The keys were usually grouped in lettered pairs, which include: (A, B), (C, D), (E, H) and (J, K). Stock GM vehicles will use one of these group of keys, and which group depends on the year the vehicle was manufactured. If a lock(s) on your GM vehicle were replaced sometime in its life, than its possible the replacement lock uses a different lettered key, so the lettered car key combination for your car will be an odd group of letters. carlocksandkeys.com carries all the GM lettered keys, so if your GM car uses an odd pair, than let us know and we will ship the correct keys to you.
GM vehicles using this type of key were assigned a letter group for 1 model year, than the next year were assigned a new lettered group of keys. This cycle continued until 1983. In 1983 GM vehicles were assigned a letter group for 4 years, than the 5th year were assigned a new letter group. This 4 year cycle continued until the key groups were phased out in the mid 1990's. The following list shows the year, and letter group assigned for that year:
1968 - (C, D)
1969 - (E, H)
1970 - (J, K)
1971 - (A, B)
1972 - (C, D)
1973 - (E, H)
1974 - (J, K)
1975 - (A, B)
1976 - (C, D)
1977 - (E, H)
1978 - (J, K)
1979 - (A, B)
1980 - (C, D)
1981 - (E, H)
1982 - (J, K)
1983 to 1986 - (A, B)
1987 to 1990 - (C, D)
1991 to 1994 - (E, H)
GM continued to use some lettered keys until 2002. For example, GM used the 'H' secondary key in the Chevrolet Camaro until 2002.
The square key is sometimes refereed to as the primary key, and is the key used to unlock/lock the ignition lock. Sometimes locks were keyed to work with the primary key, so its possible for the primary key to unlock/lock the door locks as well as the ignition lock. The round key is sometimes referred to as the secondary key, and is usually used to unlock/lock the door, trunk and glove box lock. The following is a list of names used to identify the lettered key blank:
'A' Key Blank - Primary Key - Also referred to as a B48
'B' Key Blank - Secondary Key - Also referred to as a B49
'C' Key Blank - Primary Key - Also referred to as a B50
'D' Key Blank - Secondary Key - Also referred to as a B51
'E' Key Blank - Primary Key - Also referred to as a B44
'H' Key Blank - Secondary Key - Also referred to as a B45
'J' Key Blank - Primary Key - Also referred to as a B46
'K' Key Blank - Primary Key - Also referred to as a B47
Door and trunk locks used on early GM vehicles had a lock shutter with a gate, and this gate fit into a side groove on the key when the key is inserted into the lock. Sometime in the 1970's GM stopped using the gated lock shutter and replaced it with a shutter with an open key slot. Early GM lettered keys were slightly longer than the OEM key blanks manufactured for GM today. I don't know why GM changed the length of the keys, but it was probably to save money on brass. The older and slightly longer lettered key blanks had a side groove, which was slightly longer on the older keys than the groove found on newer OEM lettered key blanks sold by GM today. If you have an older GM vehicle that uses a lock shutter with a gate, than your going to have problems inserting the newer OEM keys far enough into the lock, so that the shoulder of the key reaches the correct resting position in the lock to unlock/lock the lock. This is because the groove found on the newer OEM keys is not long enough, and the gate on the shutter reaches the end of the groove before the key is inserted far enough into the lock to correctly operate the lock. The only solution to this problem is to either increase the length of the key groove, or replace the older style lock shutter with a new version. See photo below.
Photo of all GM lettered key blanks. Notice image of lock key way below each key blank.
Photo of the older style lock shutter with gate, and the newer style with an open key slot.