Code Letter FONs were

Code Letter FONs were stopped after 1941 and any instruments made during or right after World War II do not bear any FON codes. Better to look for a combo of serial numbers, factory order numbers and any design features specific Threaded Rod Astm to the time.

There are three groupings of numbers which are used for their accuracy. The FON will even provide what number in the batch of forty guitars your instrument was.
When both numbers are present on a high grade model, please remember that the FON was assigned at the beginning of the production run, while the serial number was recorded later (before shipping). In1949, a four digit FON was used, but not in conjunction with any code
letter. His website is where you will find articles, information and useful links about vintage Gibson GuitarsArticle Source: 1ArticleWorld. The numbers are often stamped or written on the back of the instrument and seen through the lower f-hole or round soundhole. They may also be impressed on the back of the headstock. The FON is the only identification number on Gibson s low models like the ES-125, ES-140 etc.

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Lyndon is a collector of Gibson vintage guitars.) have both a serial number and a FON. Therefore early Gibson Vintage Guitars may have both a FON and a serial number. High grade models (such as the Super 400, L-5 etc.)
which do not feature a paper label. Serial numbers are not always the answer.Vintage Gibson guitar identification is easy if you know what to look for.

Factory Order Numbers (FON s) were used by Gibson to track batches of instruments in the early days when they made guitars normally in batches of forty. The serial number would be the best indication of the actual date of the guitar.

From 1952-61, the FON s scheme followed the pattern of a letter, batch number, and instrument ranking number.

For a more detailed information plus a list of serial numbers you may want to visit my website as there is too much information to share in a single article