SME is a brand name of an English company that produces "High End" tonearms and turntables, whose name has become synonymous with the industry standard headshell mount.
SME is an abbreviation for "Small Mechanical Engineering"
SME was also an abbreviation for "Scale Model Engineering"
Series II The company is notable for its 3009 and 3012 (9" and 12" respectively) tone arms which were widely adopted for audiophile and broadcast use during the 1960s and 1970s, at the higher end of the market. These arms featured a polished stainless steel main tube with a lightweight headshell, knife edge horizontal bearings, and an anti skating bias provided by a weight that hung by a nylon string. Versions were produced with both fixed and interchangeable headshells; the SME headshell mount became the defacto industry standard, and is still widely used today on consumer and especially DJ decks. Audiophile arms today tend to not use the SME mount, but this is not due to other standards replacing the SME but because audiophile arms now tend to not have interchangeable headshells at all in an effort to reduce mass and improve rigidity, though at slight expense of user flexibility.
Some cartridges were produced that mounted directly into the SME headshell mount of the arm (rather than into a headshell), notably from Ortofon)
Series III. The Series III was introduced in the late 1970s incorporating changes from the Series II models (which continued in production) covering both styling and its exceptionally thin and lightweight main tube, the entire arm being interchangeable rather than just the headshell. Although technically advanced, the Series III never achieved the market dominance of the Series II.
Series V The series V arm was developed as a medium mass arm more suited to emerging moving-coil cartridges with lower compliance than previously available moving magnet cartridges. The removable headshell was eliminated, and the horizontal knife bearing was replaced with ball bearings, both in order to provide a more rigid structure for the cartridge.
In recent decades, as with many of their competitors, the company's products have tended to move further and further upmarket. Recent products include the SME V tonearm, and extremely expensive (and consequently relatively rare) decks. The company bucked their upmarket move with the M2 tonearm which sits at the bottom of their current range .