To 99.64% of the readers, you were introduced to ESP’s explorer shaped guitars by Metallica guitarist James Hetfield. ESP made explorer shaped guitars, mostly under the Navigator brand, before working with Hetfield, but they were clones of the Gibson shapes with pick guards and control layouts.
In the late 80’s ESP made a few explorer shaped guitars for Hetfield. These include the infamous “EET FUK” guitar with the raised middle finger inlays, and one with dot inlays which was featured during the Metallica documentary “A Year and A Half In the Life of Metallica; pt. 1”. These guitars were originally known as the EX, but later became known as the MX-220II.
The designation stood for:
M - Metallica
X - eXplorer
220,000yen retail (in late 80s early 90s money)
II - 2 pickups
The MX-220II body is slightly shorter (bottom strap button to tip of headstock) and has rounder horns than the “current” explorer body. The toggle switches on these first two explorers were closer to the knobs than later explorers, and they had a unique two screw truss rod cover that mounted flush with the nut. They also feature a step where the neck joins the body, similar to a Gibson explorer, and their input jacks are round and recessed into the body.
Further revisions of the MX-220II changed the input jack was changed to mount to a plate held by four screws. The truss rod cover changed to a 2 screw Gibson style which was no longer flush with the nut but everything else stayed the same including the step in the neck.
Later in the evolution of the MX-220II, ESP removed the step at the neck joint, and a return to the recessed mounted output jack. Each of the MX series guitars (including the evolution to the MX-250II) featured ABR-1 style bridges, which have the posts mount directly into the body of the guitar. This is used instead of a Nashville style, which screw into bushings which are pressed into the guitar. It is said that the MX-220II guitars do not feature serial numbers or the circle logo on the back of the headstock. The circle logo on the headstock is not a typical feature on ESP guitars made for the Japanese market.
People found this comparison between a Gibson 1958 (the red lines) and 1976 (black lines) Explorers. Based on picture and descriptions, peope think this is a reasonable representation between the body shapes.
This new design was given the name MX-250II (and later just the MX-II, as the 250 referred to the price). The MX-250II has a slightly longer body than the MX-220II, and has sharper points. The step in the neck joint was removed. In the early to mid 90s, ESP kept the Gibson style truss rod cover and kept the flush-mounted, round input jack. Also during this revision, the pickup selector switch was moved further away from the volume pots and pickups.
The MX-250II was released in Japan with set mahogany necks, ebony boards and full mahogany bodies with poly finish. They came stock wired with dual EMG 81 pickups. Available in black with dot inlays. Order made MX250 these were available in any color for an up charge and also you could request Sperzel tuners and a few other options before it became a full custom order. These guitars could be special ordered from the USA, however they were known as the EXP Custom as the MX designation was used for a different model of guitar. These featured single screw bell shaped truss rod covers with a single screw. These all had serial numbers on the back of the headstock. ESP changed to the bullet style truss rod cover in 1995.
The only "production" Explorer ESP made for the US market were the EXP models. They came in both ESP and LTD flavors. The EXP was a bolt-on neck version of the MX-II body style. The ESP version (ESP EXP) featured rosewood fret boards, maple necks and mahogany bodies. The LTD version (LTX EXP-200) also had a maple neck with a rosewood fret board. I've heard that different years had different body material, the earlier years having alder and later years switching back to mahogany. There is also a change in position markers, the earlier LTDs had 2 dots at the 12th fret, and later models had a block with LTD engraved.
The ESP version came with 2x EMG 81s, the LTD version came stock with Duncan Designed pickups.
The LTD line also featured the EXP-300, which was a set neck explorer shape which featured a licensed Floyd Rose bridge. This guitar came with two EMG 81s as a stock option.
In 2000, ESP had their Korean factory produce the LTD MX-130. These were similar to the MX-250II, and interestingly enough, did not have serial numbers. These guitars were for the Japanese domestic market. All came from the factory with two EMG 81s and featured the same set neck construction as the MX-II. The MX-130 was available in Black, some featuring the plastic diamond plate of the Hetfield JH-2 signature explorer.
While these guitars are rare, they can be found from time to time on Ebay. These were discontinued in 2003 all had the new bullet style truss rod cover.
The first EX/MX-220II Custom inlay run was the EET FUK in 1989. It was a very small run featuring slightly smaller inlays after the 5th fret and no step in the neck. Apparently, Hetfield found out and they had to stop production. I believe less than 30 were made. There were also a few MX-250II bodies made with these inlays.
Special versions of the MX-250II such as the “Man to Wolf” Explorer were called in Japan ESP Special Interest Group. I have no idea what this means but it probably means that you had to be someone or pay a lot to get one. Former forum member EXPCustom confirmed with Ron Thorn that along with ESP a limited run of about 20 “Man to Wolf” Explorers were made. Ron Thorn inlaid the fret boards for the run. In the early 2000s one showed up on Ebay Japan. The seller wanted 10,000 US dollars for it. These had serial numbers and were all set neck with one screw bell truss rod covers identical to Hetfield's in every way. There was no custom shop logo.
Elk Skull MX250 was available from the late 90's to 2003 as custom order only. I have never actually seen one but I have correspondence E-mail from ESP of Japan from 2002 confirming me a price and time to make on an Elk Skull so I know they exist I have never seen one. This was done in the custom shop in Tokyo not by the original wood burn artist.