IBM buckling rubber sleeve



IBM buckling rubber sleeves<a class='source-link' href='/wiki?id=ibmsleeves#Sources'><sup>[ASK]</sup></a>
IBM buckling rubber sleeves[ASK]

IBM buckling rubber sleeves (or simply IBM buckling sleeves) are a tactile key-switch developed by IBM as a quiet, low-profile alternative to IBM membrane buckling springs for IBM's flagship keyboards outside of the buckling spring keyboards' primary domains. It was first employed on the IBM Personal System/2 L40SX laptop and its Model M3 numeric keypad option both released in 1991, then subsequently reused on Model M4-family Space Saver Keyboards and then modified for use on Model M6-family PS/Note, PS/55 Note and ThinkPad keyboard assemblies. Its use on portable computers was phased out by the late 1990s, however, Unicomp continued to produce this switch for its Model M4-based Mighty Mouse keyboards until the late 2000s[1]. A version of this switch was also employed on IBM's 1993-launched Model M7, M7-1, M8, M9 and M11 POS keyboards and keypads, and later POS keyboards and keypads that IBM introduced in the 2000s and Toshiba Global Commerce Solutions continues to make today.


Switch type
Sensor type
Keycap mount
Dual-clip (M3/M4/M4-1/small gauge M6/M6-1) or crosspoint (standard & medium gauge M6/M6-1)
Total key travel
3mm typical (depends on gauge)
Peak tactile force travel
Peak tactile force
~60gf (± 20gf)
Rated lifetime
10 million key presses minimum

Specifications correct for IBM buckling sleeves employed by Unicomp as of 1999[2].


IBM buckling sleeves key-switches are membrane driven and were seemingly derived from the same patents and/or copyright as membrane buckling springs as their host devices often cite 1984 as the copyright date. The sleeves are tactile and snappy and are of medium-heavy weighting just below buckling springs. They do not feature part-way actuation as a property - like membrane or conductive PCB driven rubber dome switches, the user is required to bottom out to actuate, but the experience of doing so is different to rubber dome switches and even some conceptually similar buckling rubber sleeve based switches. The key differences:

  1. Compared to rubber dome switches, the rubber component sits externally from the assembly on top of a barrel plate and is used for providing tactility and return force for the keycap only - they play no part in direct actuation. Most non-capacitive rubber dome switches are required to play a role in bridging the connection with the sensing mechanism.
  2. For IBM sleeves, a rod on the keycap or a slider in the barrel (depending on implementation) provides a solid interface to the membrane to close the circuit, meaning the mushy bottom-out feeling typically expected from low-end rubber dome key-switches is generally avoided[1].
  3. IBM sleeves are outwardly-expanding conical-shaped instead of traditionally dome-shaped and are sculpted so that the rubber at the top rim of the sleeve buckles to rest aside the bottom rubber instead of all 'squishing' at the bottom.
  4. Unlike the conceptually close Mitsumi KPQ Type switches, IBM's design lacks the conductive rubber foot on the bottom of its actuation element (keycap rod or barrel slider), eliminating another possible element that could dampen a solid bottoming out feel.


IBM buckling sleeves exist in five distinct sizes and forms (referred to as gauges) suited for different key sizes.

M3, M4, M4-1, M6, M6-1, M7, M7-1, M8, M9, M11, M-e
Most common
M3, M4, M4-1, M6, M6-1
Originally used on M3/M4/M4-1 spacebars, early M6 & M6-1s may also use this for all keys
Exclusively used on CANPOS & MCANPOS small keys
M6, M6-1
Typically for only function & nav keys, some use for all keys
M6, M6-1
Exclusively small function & nav keys
Visual comparison of IBM buckling sleeve gauges<a class='source-link' href='/wiki?id=ibmsleeves#Sources'><sup>[ASK]</sup></a>
Visual comparison of IBM buckling sleeve gauges[ASK]


Model M3/M4/M4-1 type (1991-2010)

The original implementation of IBM buckling sleeves was introduced with the March 1991-launched[3] IBM PS/2 L40SX laptop and its Model M3 numeric keypad, originally manufactured by IBM US. The following year, the L40SX keyboard assembly was adapted for use with the IBM PS/2 CL57SX (made by IBM US[4] and Lexmark[5]) laptop and introduced onto desktop keyboards for the Model M4 (without TrackPoint) and M4-1 (with TrackPoint) Space Saver Keyboards (made just by Lexmark until 1996). Key Tronic briefly produced 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. The principal feature of this earlier type of IBM buckling sleeves is the keycap mount, which features two plastic clips on either side of the keycap that retains the keycap on the barrel plate. As described in Design, the keycap's central rod is used for actuation[1]. This implementation also exclusively uses standard gauge sleeves, even for the smaller-sized keys.

Model M6 type (1992-1996)

IBM buckling sleeves received its first and largest revision in October 1992[6] with the IBM ThinkPad 700 series and PS/55 Note C52. Along with the keyboards used for the ThinkPads 720 and 350 series, and PS/Note 425 series, these keyboard assemblies were designated Model M6 by IBM and feature a radical change in the switch's actuator design. Namely, the membrane is now pressed on by a barrel-fixed slider instead of a rod on the keycap, and the keycap itself now has a more traditional form of mounting (crosspoint) that doesn't require clips on the edges. The barrel slider colour is brown and its mount is quite minimalistic/skeletal. Lexmark itself also used the M6 design for a number of its own laptop (Lexbook) keyboard assemblies and some laptop keyboards it made for other companies. For the alphanumeric and modifiers keys, the sleeve itself is unchanged from M3/M4/M4-1 type (ie, standard gauge) and is fully interchangeable. However, for the smaller function and navigation keys, medium gauge sleeves are now employed. A select few M6s may use small gauge sleeves for their function and navigation keys. All known M6 keyboards were exclusively produced by Lexmark.

Early POS type (1993-2002)

The third implementation of IBM buckling sleeves was introduced in June 1993 with the Retail series of POS (RPOS) keyboards introduced for the IBM 4694 POS Terminal[7]. These keyboards were namely the IBM Models M7, M7-1, M8, M9 and M11 produced by Lexmark and Maxi Switch. This type is barrel slider actuated just like M6 type but the barrel slider is black instead of brown. The keycap mount itself is unchanged and it's possible to mount M6 (and later M6-1) keycaps onto an RPOS keyboard with this type. RPOS keyboards only ever used standard gauge sleeves.

Model M6-1 type (1993-1999)

The Model M6-1 type is a modification of M6 type introduced in September 1993[6] with the IBM ThinkPad 750 series. This version is only a slight revision compared to the M6 type, introducing the change in barrel slider colour made by early POS type and larger membrane flex connectors. Instead of a skeletal brown slider, M6-1 employs an always black but either the same skeletal (just like early POS type) or a more 'filled-out' slider (but still accepts the same keycaps). The M6-1 was also more widely adopted than its predecessor, with the ThinkPads 360 series, 370C, 355 series, 755C series, Power Series 850, 365 series and RS/6000 Notebook 860 all employing Model M6-1 keyboards. There are some other non-ThinkPad IBM laptops and Lexmark OEM designs that were M6-1 based too. M6-1 was produced by Lexmark and later Key Tronic[1] starting 1995 Q4, however, these should not be confused with Key Tronic's own take on the buckling rubber sleeves design used on the ThinkPad 701C/701CS TrackWrite keyboard[8]. The use of gauges is the same as M6.

Late POS type (2002-present)

Late POS type buckling sleeves are the latest IBM buckling sleeves design and the only one still in production. When IBM shifted RPOS production from the Americans to the Far East in the early 2000s, IBM opted to alter the keycap design back to a rod-actuated design like M3/M4/M4-1 type but still with some differences. Instead of using two clips to hold the keycap in place, the rod itself acts as the clip securing the keycap in its barrel. Late POS type keycaps are known for being hard to remove without damaging them. Whereas early POS type buckling sleeves were produced by Lexmark (USA) and Maxi Switch (Mexico), late POS type was produced by XAC (Taiwan) and XSZ (China) during the IBM era. In 2008, IBM introduced the Modular series of POS (MPOS) keyboards[9] that were an evolution of RPOS designs and retained the use of late POS type buckling sleeves. In 2012, Toshiba TEC bought IBM Retail Stores Solutions[10], forming Toshiba Global Commerce Solutions and seemingly taking production of RPOS and MPOS keyboards in-house. As with early POS type versions, RPOS keyboards only used standard gauge sleeves, however, IBM CANPOS and IBM/Toshiba MCANPOS keyboards use medium-tall gauge sleeves for their half-height keys.

Host devices

M3/M4/M4-1 type host devices

More info: Model M3 PS/2 L40SX Numeric Keypad, Model M4 & M4-1 Space Saver Keyboard, Model M4 & M4-1 Space Saver Numeric Keypad

M6 type host devices

Early POS type host keyboards

More info: Model M7, M7-1, M8, M9 & M11 Retail POS Keyboards

M6-1 type host devices

Late POS type host keyboards

More info: Model M-e Modular 67-Key POS, MANPOS & MCANPOS Keyboards


Further reading & resources


Wiki pages


ASK. Admiral Shark's Keyboards original content. License/note: CC BY-NC-SA 4.0.

  1. ASK - Revealed: The Story of the Model M4 family [accessed 2021-11-18].
  2. Unicomp - The Mighty Mouse 84 Key [accessed 2021-12-31].
  3. IBM - THE IBM PS/2 MODEL L40 SX SYSTEM AND FEATURES [accessed 2022-06-14].
  4. ASK - Revealed: IBM Model M3 & M6 laptop buckling sleeves keyboards#CL57SX [accessed 2022-06-19].
  5. Ardent Tool - PS/2 Model CL57 SX [accessed 2022-06-19].
  6. ThinkWiki - ThinkPad History [accessed 2021-11-18].
  7. IBM - IBM 4694 POS Terminal Model 001 Brief Description of Announcement, Charges, and Availability (#193-150) [accessed 2022-04-23].
  8. micrex22 - ThinkPad Keyboards and Switches [accessed 2021-11-18].
  9. IBM - IBM SurePOS 300 machine type 4810 offer new point-of-sale keyboards [accessed 2022-06-19].
  10. IBM - Toshiba TEC to Acquire IBM's Retail Store Point-of-Sale Solutions Business; Agreement Allows Both to Tap Growing Smarter Commerce Opportunity [accessed 2022-06-19].