Gibson used Factory Order Numbers (FON) on some of their guitars from about 1908 to 1961. Many times you will see both a factory order number and serial number. The FON was stamped for each batch in production and each instrument in the batch during the early stages of the build.
The FON can be very helpful dating the instrument as that might be the only marking. They can also be used together with the serial number to more precisely date the instrument.
Gibson used four different patterns of FON’s through out the years.
The first FON’s are usually ink-stamped on the neck block inside the body and have of a three to five digit number with no suffix
Alphabetical FON: 1935-1942
A for 1935
B for 1936, and so on
This method stopped around 1942 .
FON after WW II: 1949-1952
After WW II FON’s were hit or miss and not very good for dating or not present on the guitar. When present they were rubber stamped on neck block or on back of the headstock with numbers from 100 to 9999.
Alpha FON: 1952-1961
Around 1952 Gibson went back to the a first letter pattern
The first letter used in
1952 was Z
Y in 1953, etc.
Then lastly Q in 1961 which is very rare to see.