By Paul Alcantara
Some of the Gibson 17-inch archtops and Super 400s shipped between 1935 and 1940 have a fractional number handwritten on their interior label (usually on the lower left-hand corner). Examples that we have encountered include 1″, 1 1/8″ and 1 ¼”. Musician and archtop collector Tony Marcus reports having come across an L-5 with ‘1 ½-inches’ written on its label: “These have both taller bridges and thicker tops than the 1-inch ones,” he adds.
Various theories have been advanced to explain the fractional numbers and below, we outline several of these, listing their strengths and weaknesses.
The fractional number, in this case one inch, is hand written on the lower left, next to the letter G of Gibson
This label has the fractional number one and one quarter written on it
This label has the fractional number one and one eighth
Bridge height
The commonest interpretation suggests that the fractional numbers refer to the height of the bridge when adjusted to provide whatever Gibson regarded as an acceptable action. In other words, the number enabled the factory worker stringing the guitar and carrying out the final set-up to fit the correct bridge. “It seems exceedingly likely that the numbers refer to the bridge height,” says Tony Marcus.
It may be significant that the fractional numbers appear in 1935 with the introduction of Gibson’s new 17-inch ‘Advanced’ archtops. Indeed, we have never seen the numbers on a 16-inch L-5. Evidence of surviving examples suggests that the company was experimenting with the top carve at this time with earlier 17-inch archtops having a flatter arch. This would explain why all of Gibson’s archtop guitars weren’t designed to accommodate the same height bridge.
It may be significant that most of the early examples that we have come across are marked 1″ – and a little later 1 ¼” – while the first 1 1/8″ appears on the label of a L-5 shipped in 1937. From this point on, virtually all examples that we have encountered are marked 1 1/8″. If the numbers do, in fact, reflect the arch of the top, then Gibson seems to have standardised the top carve by the late 1930s.
Pros
Gibson’s catalogue Y of 1937 offered replacement bridges of three heights: 1 5/16” (item 528), 1 1/8” (item 523) and 1 3/16” (item 525). By contrast, catalogue W, which was issued in 1934 (prior to the introduction of the Advanced L-5) only lists one replacement bridge for the L-5, which is 1 1/8″ high.
Gibson’s Catalog Y
Cons
1. If the fractional numbers indicate the type of bridge to be fitted, why aren’t they written on the labels of all Super 400s and 17-inch archtops shipped from 1935 through 1940?
2. The 1 1/8″ bridge is the only catalogued replacement bridge that corresponds to the numbers on the labels.
3. We have come across several late 1930s parallel braced L-5s that have the fractional numbers on their label (according to dealer/collector John Stewart, who has specialised in vintage archtop guitars, a lot of the early parallel braced 17-inch Gibson archtops appear to have used the earlier tops—i.e. with a higher arch – so this may not be a contradiction).
Top blank
Another suggestion is that the fractional numbers refer to the thickness of the top blank prior to carving. This would enable Gibson to keep track of specific guitars should they be returned to the factory for repair.
Pros
We know that Gibson built archtops with a ‘thick’ or ‘thin’ top for a time. This applied to both 16 and 17-inch L-5s and was occasionally noted in the ledgers. It isn’t mentioned in any Gibson catalogue or promotional material, so presumably wasn’t available as a customer option.
Tony Marcus comments: “While it’s impossible to truly know what the original arching looked like on an 80-year-old guitar, all of those early Advanced Models had flatter arching, to the best of my knowledge but of course, it’s more likely for there to be some sinkage in the thinner ones.”
Cons
1. Though the numbers are only found on 17-inch archtops and Super 400s shipped between 1935 and 1940, they don’t appear on 16-inch L-5s shipped during the same period despite the fact that some of these were also listed with a ‘thick’ or ‘thin’ top.
“Having measured several Gibson archtops with the ‘mystery numbers’ I question this theory,” says John Stewart. “The top of the guitar is glued to the top of the kerfing and the binding rout goes below that glue joint. Therefore, if one measures from the inside of the binding to the highest point of the arch, the number will be around 1/16th” longer than the actual thickness of the carved out top. None of the tops I measured that way were anywhere close to 1”. All of them could easily have been carved from a 1″ billet. So, unless the tops were carved differently (different arching) due to excess thickness, it doesn’t add up to me.”
Gibson’s catalogue X of 1937 states “The fine grained, white spruce is sawed to blocks 1″ thick by 18″ wide by 25″ long”.
X bracing
Could the numbers refer to an aspect of the guitar’s top bracing? Perhaps Gibson was experimenting with a different position for the intersection of the X brace or the width of braces themselves and wanted feedback as to which bracing pattern produced a sound that players preferred? This would explain why the numbers only appear on a limited number of guitars, something that the bridge height idea doesn’t.
Pros
The numbers start to appear with the introduction of X-bracing in 1935 and disappear shortly after Gibson switched back to parallel top bracing in 1939.
Cons
A problem with this idea is the fact that the fractional numbers can be found on the labels of guitars shipped after X-bracing was abandoned.
Other theories
“I have often wondered if the numbers might reflect a setting on a machine – a carving machine for instance?” says John Stewart. “It might be some technical item that we could never interpret by observation of the finished product.”
Conclusion
We spoke to Joe Spann on this topic a few years back and he replied: “After receiving your query, I examined the Gibson material here in the Gruhn Archives as well as in my own personal collection. I found no contemporary document which supplied any direct information related to the question. These documents include materials which Gibson produced for public consumption, as well as internal factory paperwork.”
Nevertheless, the fractional numbers do appear to be related to some sort of experiment that Gibson was conducting with its 17-archtops and Super 400s in the mid to late 1930s – though what exactly that experiment was remains to be discovered.
If you have any information on what the mystery numbers mean please contact us here!