First introduced in 1989 as the “Mumbo,” the M Frame has long been a staple in the Oakley line-up and will likely endure for years yet to come. But while the frame shape has more or less remained constant, the iconic sunglasses have seen some tweaks through the decades.

The initial release included 3 frame colors (white, black, and neon yellow) and 3 lens styles—the V, 67, and Hybrid. Due to some legal grumblings by US clothing company, Mambo, the Mumbo was changed to the M Frame, the frame’s color selection expanded, and new lens shapes were introduced. Among those was the Strip, Sweep, and Heater in 1991, followed by announcements of the Strike and Slash to come in Fall '91 and Winter '91 respectively. By 1993, the Strip, V, and 67 had all been phased out.

A name change rarely accompanied the changes and updates, so here’s a break-down on what to look for to determine which era of M Frame you own:

Sketch of Oakley M Frame Design 1989

Although the Mumbo and M Frame have different names, the only real difference between the two is the packaging they came in. Since they have the same traits, they will be treated as one era.

These are recognizable by:

  • The classic “Oakley” logo on the temples
  • The ear socks extend to almost the very ends of the stems and are flat and boxy
  • Hammered stems (A sharp bend in the stem at the temple)
  • OEM lenses did not have a logo on them
  • The Mumbos and earliest M Frames also had the taller Blade nosepiece, and the lenses were cut differently to accommodate this

*Without packaging, the only way to know if they’re true Mumbos is if they’re neon yellow. Both the white and black continued to the M Frames, but the neon yellow is exclusive to the Mumbo.

Sketch of Oakley M Frame Design 1993

Please note: Pictured is a Slash lens but the frame is from the 1994 era. "Oakley" would still have been present on a 1993 M Frame, not an "O."

This year saw the edition of the Slash lens, which came in the same basic M Frame, but with a few additions:

  • Foam lining across the brow to help mop up sweat
  • A strap that connects to the frames as earsocks
  • The Slash lens from this era has round perforations lining the top of the lens for venting

October 2017 Update: After further investigation, I cannot confirm using original source material that 1993 was the true release year of the Slash. An Oakley advertisement from 1991 contains an announcement citing the release of the Slash and Strike in late 1991, but I cannot confirm the existence of promotion and sale of either lens until a 1993 advertisement. 

Sketch of Oakley M Frame Design 1994

The changes in the 1994 version have prompted what people often refer to as 2nd Gen M Frames. Although quite similar to the earliest version of M Frames, these can be identified by:

  • Classic logo replaced with the raised Oakley elliptical icon (made of molded plastic)
  • Trademarked “HammerFang” stems, which lengthened the stems past the ear socks
  • Reinforced hinges
  • Oakley classic logo etched into the top of the lens, above the nose bridge

Sketch of Oakley M Frame Design 1996

This year included the introduction of new styles of M Frames — the Baseball, Cricket, Golf, and Tennis lines and the Pro M Frame, as well as changes to the standard M Frame.

  • Hammer stems far less pronounced on the interior of the frame
  • New wing design
  • Ear socks shape is now rounded, designed for better contact with the head
  • Elliptical icon on wing, still molded plastic
  • Pro M Frames also introduced, which feature a unibody and no hinges
  • Straight stems are introduced with the Baseball line-up to accommodate batting helmets

Sketch of Oakley M Frame Design 1999

Often referred to as the “New” M Frames, these frames look almost identical to the 1996 version with a couple of subtle differences:

  • Wings shaved down slightly
  • Elliptical metal icon accents replace the molded plastic icons

Sketch of Oakley M Frame 2002

Oakley introduced the short-lived Magnesium (Mag) M Frame. Similar to the M Frame in size and general shape, the Mag M Frame is easily identified by:

  • Frame material is magnesium, not plastic
  • Spring hinges
  • Hinges are placed after the icon (hinges on the M Frame are in front of the logo)
  • The front center of the frame features 2 curved vertical lines and two recessed screws

Sketch of Oakley M Frame 2006

In 2006, Oakley introduced another member to the M Frame family named the M Frame 2.0. The intention of this frame was not to replace the popular M Frames, but to provide the military with a standard issue ballistic M Frame that could better accommodate military use. The 2.0 has the same lens shapes as the M Frames, but features obvious design changes:

  • Ridges along the top of the frame
  • Plastic molded icons always the same color as the frame
  • Wide, flat stems without hammers or wings
  • Temple design features 4 ridges
  • Removable center clip

Sketch of Oakley M Frame Design 2012

After receiving feedback, Oakley tweaked its M Frame 2.0s in 2012 and the result was the M Frame 3.0s which can be identified by:

  • Thinner arms than the 2.0s
  • No earsocks to better accommodate fitting beneath a helmet and communication equipment
  • Smaller temple design than the 2.0s
  • Hinged top center clip
  • Larger lenses for increased coverage

Sketch of Oakley M Frame 2014

The most recent evolution in the M Frame family is the M2. While still staying true to the basic shape of the M Frames, there are obvious differences to set the generations apart:

  • The wings are more angular and can be removed
  • Oakley icon is the same length as previous generation of M Frames vertically, but is shorter horizontally
  • The top of the frame features contoured lines
  • The ear socks now run from the wings to nearly the ends of the stems, with a 1¼ inch break at midpoint on the top of the frame
  • Stem length is nearly an inch shorter
  • Stems feature perforations to accommodate a strap
  • Ridge on the inside of the frame in the center above the nose
  • The hammer stem is now totally gone, with no indentation or curve in the stem

At the time of publication, Oakley only has one lens shape for the M2s, which is certainly a departure from the original concept. While lenses for the 1999 M Frames can fit in the M2s, it's a loose fit.