Editing IBM buckling rubber sleeve (section)

==Models M3, M4 & M4-1==
[[File:M3-m4 components.jpg|thumb|right|M3/M4/M4-1 type switch components]]
The original implementation of IBM's buckling rubber sleeve was introduced with the March 1991-launched IBM PS/2 L40SX laptop and its Model M3 numeric keypad option. This variant of the switch is actuated by a rod on the keyboards' keycaps that descend through given key positions barrel to press on the membrane. The L40SX keyboard assembly was repurposed for the IBM PS/2 CL57SX laptop and the Models M4 (without TrackPoint II) and M4-1 (with TrackPoint II) discrete keyboard. IBM Information Products Corporation originally produced the switch and the keyboards that used them, however, this production soon became Lexmark-based after the divesture of the aforementioned IBM division. Key Tronic briefly produced Model M4s shortly after Lexmark's exit from keyboard production and Unicomp finally continued producing and selling a keyboard based on them called the Mighty Mouse until 2010. During the 19 years of production and sale, the switch design remained unchanged. Another common feature of keyboards that use this original flavour of IBM buckling rubber sleeves is that the keycap mounts onto the keyboard via two clips on either side of the keyboard<ref name="sharkm4article" />.