Around the middle of 1964 major changes occurred. The info below is very useful for dating a Gibson guitar in cases where serial numbers were repeated or unclear.
1. Neck width at the Nut was reduced from 1 11/16 inches to 1 9/16 inches (you will see cases of 1 10/16 inches during this transition year.
2. Most Hardware moved from Nickel plated to Chrome, this included bridges, tuners and tailpieces.
3. Most serial numbers moved from 5 digits to 6 digits.
4. Kluson Tuners were stamped with 2 lines down the back instead of one line down the center of the back with the words Kluson Deluxe.
5. By 1965 the Stud Tailpiece on the Gibson Es-335, Es-345 and ES-355 were removed and replaced with a Trapeze tailpiece.
There is more information here on the our Guitar identification Page.
1968 -69 were dark years for Gibson and the Norlin Corporation buy out began. Gibson needed revenue and to use up old parts. Less than perfect tops used to make the J-45 and B-25 were sprayed a solid color of red or black and a few brown . A white screwed down pickguard was used. Many of the instruments were 4 piece tops and marked seconds. Late in 1968 the bridge was reversed with the belly facing down , and the Gibson logo on the pickguard was removed. There is more Gibson Acoustic Flattop Model Information here.
The first Pickguards on the Telecaster were one ply black. The earliest ones were a fiber material then later made of bakelite with 5 holes for screws. In Late 1954 the single ply white pickguard was introduced.
The Telecaster Custom was introduced in 1959 and had a 3 ply white/black/white celluloid pickguard with 5 screw holes. This is also used on custom color Telecasters. The single ply white pickguard remains standard equipment on the blonde Telecaster.
In mid 1959 all the telecaster pickguards have 8 screw holes.
In mid late 1963 all the telecaster models have the 3 ply white/black/white pickguard, the celluloid “Green Guard” is dropped after 1964 and replaced with plastic.
Gretsch Serial numbers can be confusing an unclear at times. Here are some helpful ways to date them from unique features of the era.
The Half moon sometimes referred to as thumbprint or Neo-Classical appeared in 1957. These came on the higher end Gretsches. So if you see a Gretsch with these inlays you know it was made in 1957 or later.
The slanted script logo was used pre 1950. In 1954 the T roof logo (long top line over the T in Gretsch) was used until around 1981.
The Zero fret was used on all Chet Atkins Models starting in 1959, then in 1962 it was used on most all the other models like the 6120, Monkees . So Zero fret indicates post 1958.
Metal name plates that were engraved started being used around 1958 and appeared on the White Falcon, Nashville (1966), White Penquin (1959). In 1965 it appeared on the Tennessean. Earlier models had no name plate so this is a good dating method when serial numbers are unclear.
Fake F holes on some models:
In 1957 Gretsch used simulated F-holes on the Country Gentleman, then in 1962 the F-holes are just painted on the guitar.
The Padded Back was fazed in around 1962, and is a normal stock feature on the White Falcon, 6120, and 6122 and Country Club models.
You can look up vintage Gretsch Serial Numbers here.
Martin guitars have a two part designation the body size a hyphen then the model located up inside the guitar on the block where the neck and body meet.
The model designations are 15, 17, 18, 21, 28, 35 and 45.
Models 15, 17, 18 post 1917 are Mahogany back and sides. The 15 and 17 has a mahogany top. The 18 style’s top is made of spruce.
Models 21, 28, 35 and 45 are rosewood back and sides with a spruce top.
The size designation at widest point (lower bout) measurements is as follows:
2 12 inches
1 12 3/4 inches
0 13.5 inches
00 14 inches
000 15 inches
D 15 5/8 inches
Here is a link to my Martin Photo Gallery showing different Models and sizes.