Gibson L-5

1928 or 1930 Gibson Master Model L-5 Guitar
L-5 acoustic guitar, lower bout width: 16" (played by Maybelle Carter). Called "the most important single guitar in the entire history of country music", by George Gruhn.
There is controversy about its date. Commonly said to be a 1928 instrument, but researcher Joe Spann concluded that it couldn't have left the factory earlier than April 1929 and was shipped January, 1930.
 
L-5 Advanced acoustic. (after 1934)
lower bout width: 17"
c.f. Super 400 introduced in 1934 has a wider body, lower bout width: 18"
Known prototypes between both models
1. Intermediate form of these models is known:
1935 L-5 Special with a Special 400-style/18" body
2. One of the earliest Super 400 (serial 91809) remains confusion of model name notation: "Deluxe" and "L-5" on the label, "Super L-5" on the truss rod cover, and "Super 400" on the neck heel plate.

The Gibson L-5 is a hollow body guitar first produced in 1923 by the Gibson Guitar Corporation, then of Kalamazoo, Michigan. One of the first guitars to feature F-holes, the L-5 was designed under the direction of acoustical engineer and designer Lloyd Loar, and has been in production ever since. It was considered Gibson's premier guitar during the big band era. It was originally offered as an acoustic instrument; semi-acoustic models became available in the 1940s.