The Yamaha Corporation (ヤマハ株式会社, Yamaha Kabushiki Gaisha) is a multinational corporation and conglomerate based in Japan with a wide range of products and services, predominantly musical instruments, motorcycles, power sports equipment and electronics.
 Yamaha began using the "SG" (solid guitar) prefix for their solid bodied guitars when they introduced their first solid-body model in 1966 and continued using the SG prefix up until 1981.
 There were three SG eras - the first era SGs, lasting from 1966 to 1971, saw guitars with double cut-away bodies with similar features to the Fender Jazzmaster. These guitars had single digit suffixes - like SG-3, SG-5 and SG-7.
 Features:  
- the round Yamaha logo on the headstock is not a decal, it's a die cast metal piece with chrome tuning forks (the Yamaha logo) raised above a black background.   You can turn it with your fingers on my guitar but it doesn't come off  
- you can also see in the picture that the Yamaha brand name appears on the neck plate. This is also chrome and black but is a stamping not a casting. And this isn't actually a neck plate because it doesn't hold the neck on. If you remove the four screws this plate comes off, you will then see the actual neck plate which has four larger screws holding the neck on. The neck plate has a rectangular "window" in it to allow you to access the truss rod through a hole through the body into the back of the neck (that's right, the truss is accessed through the back of the neck).  
- All three pickups are identical. They have adjustable pole piece screws. The black and silver areas that you see are actually the tops of the pickup bobbins themselves. The black and silver areas are covered by a domed clear plastic piece. I took the guitar apart a few years ago to give it a good cleaning. I found that the pickups are not held in place with springs at the height adjustment screws like normal pickups, but instead had a large foam rubber block under the body of each pickup.  
The fretboard is quite thin. Thin enough that the side dots are actually located on the split line between the fretboard material and the wood of the neck. The guitar's serial number is stamped directly into the fretboard between two of the lower frets.  
- Yamaha was obviously proud of this guitar, and put their name and logo all over it. Besides the Yamaha name on the tuning machines, it has the Yamaha decal and die cast logo on the headstock, the name and logo on the neck plate and the name and logo are molded into the bridge pickup ring between the two bridge pickups.  
- The SG2 and SG3 were Yamaha's first electric guitar models, and finish details (as described above) are amazing for a 1965 Japanese guitar. If I lay it down next to my Strat, the Strat looks like a bargain basement model by comparison. Later 1960s models in Yamaha's SG series have far cruder appointments.  
- As was already noted, the bridge has roller saddles and each saddle is height adjustable. The bridge also has the normal coarse height adjustment screws on each end. There are two sheet metal springs on the ends of the bridge pinching the saddles together so they don't move side-to-side.  
- The guitar shown here has either a metal or black plastic nut, mine is white plastic. There is, of course, a zero fret.  
- The string tree is also a good quality chrome plated die casting, not a metal stamping like many guitars of the period.  
- The main knobs are chrome-plated metal with plastic skirts. As for the roller controls, the mysterious 3rd thumbwheel nearest to the bridge pickup is a balance control for the two bridge pickups. This functions whether the slide switch is in the up or down position.  
- The remaining two thumbwheels are just like their Fender counterparts; they're a volume control and a tone control that override the main volume and tone controls when the slide switch is in the up position.  
 Supposedly most of them were sold in Japan, and only a few were exported to the US.
 Yamaha
SG Series
SG-5
Japan
Available 1966 to 1971
Neck: Mahogany.
Fingerboard: Rosewood.
Number of Frets: 22.
Scale Length: 24 ¾ inches.
Options: Double Cutaway
Bolt-On Neck
Chrome Hardware
2 Volume Controls
2 Tone Controls
3-way Pickup Selector Switch
 The 6-string Yamaha electric guitar made in 1966 / 22 frets / Gold plated knobs and tunes / Weight: 3.5 kg ( 7.7 pounds ) / The entire length: 103 cm ( 40.5 inches ) / Color: Sunburst / The 3-way toggle switch is similar to the Mosrite Ventures model / A unique body shape / There is no other body shape like this one.
 The SG7 was the first Yamaha electric guitar unleashed in 1966. Featuring a peculiar asymmetrical body with an elongated horn on the treble side and a hockey stick style headstock, the guitar was designed with the input of Japanese Eleki legend Takeshi Terauchi.
 The SG7 was reissued in 2000 as the SGV300 in a range of finishes: Black, Canary Yellow, Metallic Red and Pearl Green. A deluxe SG800 model was also released in the same year. It’s become a modern surf classic.
 The Yamaha RGX and RGZ electric guitars Series are manufactured by the Yamaha Corporation and bear a close resemblance to the Ibanez RG series, the Jackson Soloist and other "superstrat" enhanced copies of the Fender Stratocaster. These Taiwan-made instruments were introduced in 1987.
 RGX Series guitars often have 24 or more frets and a bolt-on neck. Some high-end models use a neck-through-body design.  Some come with Yamaha active pickups, two single coils and one humbucker.
 Most of these instruments were generally known as RGZ, including the RGZ820R, a custom plaid graphic model with two humbuckers and a Floyd Rose licensed locking tremolo, played by rock guitarist Blues Saraceno.
 The RGX guitars were upgraded in 2003 with a 3D headstock sporting a 3+3 tuner layout and a piezo bridge option for acoustic-like tones. Famous endorsees of the RGX/RGZ guitars included Blues Saraceno and Ty Tabor of King's X, who got his namesake RGX-TT and RGX-TTD6 signature models in 2000.
 Features one single Pickup: a humbucker, in the bridge. Its bridge was a non-licensed "Fender Synchronized tremolo"'s clone. It had 24 frets.
 Features two humbucker pickups, one tone knob, one volume knob, and a three-way pickup selector.
 Features H-S Pickup's layout design: a humbucker the bridge for fat lead tones and a single-coil in the neck, for treble (and traditional Stratocaster) tones. It had a version of Floyd Rose tremolo's bridge, and a 24 frets scale.
 Yamaha RGX 312 models were produced from 1987 to 1993. Amazing versatility available from its  H-S-S (humbucker/ single coil / single coil) pick-up configuration. The neck is straight with low action and a wide fretboard. The RGX312 (1987–1988) is a double cutaway rock style guitar available in Red, Black, or White finish.
 Specifications:
 Original List Price: $429.00
 Neck - single coil
Middle - single coil
Bridge - Humbucker
Construction:
 String length: 628mm
Nut width: 41mm
 The RGX312II (1988–1993) is a double cutaway rock style guitar available in Red, Black, White, or Silver Pearl finish. The guitar is set up with Yamaha pickups as follows:
 Original List Price: $449.00
Neck - single coil
Middle - single coil
Bridge - Humbucker
Construction:
 String length: 628mm
Nut width: 43mm
 A good reliable guitar that has good tone for clean when played through the single coil and sounds fantastic for distortion on the humbucker.
 All of these guitars have in common: a Basswood body, black Hardware (bridge, tuners etc.), double locking tremolo system, 24 fret neck, a half-painted headstock, 24 3/4" scale, and recessed input jack.
 S-S-S pickup configuration
 Satin finish three piece 24-fret bolt-on maple neck with maple fingerboard. 
RM-Pro vibrato system with pitch rise adjustment.
Height-adjustable locking nut.
S-H pickup configuration, with angled neck single coil.
3-way pickup selector switch w/ coil tap and three way tone(?) switch.
Single 250k volume pot.
 Dates of manufacture:  1994 - 1998. Production of the RGX 120 D began in 1994 and ended in 1998. Features H-H Pickup's layout design: a humbucker in the bridge for fat lead tones, and another one in the neck, for traditional treble tones. Its bridge was a non-licensed "Fender Synchronized tremolo"'s clone. It had 22 frets.
 Manufactured by the same time of the RGX 120 D model, it's essentially the same guitar, but with a different pickup's layout design: H-S-H style. A humbucker the bridge for fat lead tones, a single-coil in the middle position for traditional Stratocaster tones and a humbucker in the neck, for treble tones. It had the same non-licensed "Fender Synchronized tremolo"'s clone bridge. It had 22 frets.
 Manufactured between 1994 and 1998, features H-H Pickup's layout design: a humbucker in the bridge for fat lead tones, and another one in the neck, for traditional treble tones.  It had a version of Floyd Rose tremolo's bridge. It had 24 frets.
 YAMAHA produced the RGX 421 D between 1994 and 1998. Features H-S-H Pickup's layout design: a humbucker the bridge for fat lead tones, a single-coil in the middle position for traditional Stratocaster tones and a humbucker in the neck, for treble tones. It had a version of Floyd Rose tremolo's bridge. It had 24 frets.
 The RGX 621D was discontinued in 1995. The RGX 621D's pickups were directly mounted to the guitar's body. The RGX 621D model had a custom scalloped fretboard from the 20th to the 24th frets. This feature was intended to help fast and accurate fingering.
 The RGX 621D had a Yamaha height-adjustable locking nut. This allowed players to customize the action and feel of their guitar based on playing style and string gauge preference.
 The body was alder. The neck was maple, with 24 fret rosewood fingerboard.
 Pickups were two humbuckers (neck and bridge positions) and one single coil (middle position). The controls were a five position pickup selector and master volume and master tone controls.
The bridge was a TRS-Pro locking tremolo. All hardware was black chrome finished.
 Finish options were Antique Sunburst Satin, Black, Blue Metallic, Red Metallic and Natural Satin
 The RGX 820 R was made between 1993 and 1995.
 The RGX 821 was made between 1994 and 1996. The RGX 821 / 821D was one of the most expensive guitars in the Yamaha RGX series, selling for around $1000 when new. The RGX 821 pickups were directly mounted to the guitar's body. The RGX 821D and 621D model variants had custom scalloped fretboards from the 20th to the 24th frets. This feature was intended to help fast and accurate fingering.
 The RGX 821D had a Yamaha height-adjustable locking nut. This allowed players to customize the action and feel of their guitar based on playing style and string gauge preference.
 The body was alder with figured Veneer. The neck was maple, with 24 fret rosewood fingerboard.
 Pickups were two humbuckers (neck and bridge positions) and one single coil (middle position). The controls were a five position pickup selector and master volume and master tone controls.
 The bridge was a TRS-Pro locking tremolo. All hardware was gold plated.
 Finish options were Antique Sunburst, Black Burst, Faded Blue and Violet Burst.
 YAMAHA began making the RGX 121 S in 2002
 The RGX 420 S was introduced in 2003. The Yamaha RGX 420 is an electric guitar that, so far, has been released two times in versions "S" and "dz", featuring different paint-finishes but all the same mechanics and electronics.
 YAMAHA manufactured the RGX 420 SD6 (Drop 6) between 2001 and 2003
 Dates of manufacture:  2005. The RGX 320FZ was introduced in 2005
 YAMAHA began making the RGX 520FZ in 2005.
 A typical fat strat, this guitar features H-S-S (humbucker/ single coil / single coil) pick-up configuration and had a 22-fret, and a non-licensed "Fender Synchronized tremolo"'s bridge. Body with a Fender-style plastic pickguard.
 HSH pick-up configuration, alder body, 24-fret neck, and TRS-101 locking tremolo. 
 Dates of manufacture: 1989 - 1991 
The Yamaha 611M was a superstrat style electric with an alder body and bolt-on maple neck. It had a 24 fret maple
fingerboard with black dot inlays. The lower part of the headstock was carved. It had superstrat style hardware finished in black, including a double locking Yamaha RM-Pro II tremolo system. Pickups were a diagonally mounted single coil at the neck and a humbucker at the bridge. Controls were a single volume knob, three-way pickup switch, coil splitter, two mini switches for the pickups. It came in red, black, white or yellow colors.
 First launched in 1990, the Yamaha Pacifica series was driven by the California session scene of the day-where versatility, performance and individuality were key. The series has become one of the company’s best-selling entry-level electric guitars.
 The RBX Series are the equivalent bass versions of the RGX line. Introduced in 1987, these Taiwanese-made basses came with active or passive circuitry, a variety of pickup configurations and the choice of 4-string, 5-string, fretted, fretless and left-handed versions. They featured a bolt-on 22 fret maple neck with a rosewood fingerboard and abalone dot inlays, a pointed headstock with 4-in line tuners (4+1 tuner layout on the RBX5 and RBX755A 5-strings), except for the RBX800 and RBX1000 which feature 24 frets and a deep-joint bolt on neck (just the RBX1000 had the deep-joint). Only the RBX550 and RBX600 came with an optional maple fingerboard with black dot position markers (RBX550M, RBX600M). The RBX range has been updated in 1998 with a new body style, a 3D headstock with 2+2 (4-string) or 3+2 (5-string) tuner arrangement and a two-octave rosewood fretboard. The RBX6JM and RBX-JM2 6-strings topped the line, endorsed by Dream Theater bassist John Myung, the latter using a single custom-wound Seymour Duncan SMB-6A humbucking pickup, black hardware, an active 3-band EQ and a 24-fret rosewood fingerboard with oval abalone dot position markers.