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Fujitsu FES-301



FES-301 is Fujitsu’s full-travel leaf spring switch type. Fujitsu responded in 2020 that FKB2500 Series keyboards use FES-301E switches, where “E” denotes “ergonomic” (likely indicating DIN compliance). This would make FES-301 the original full-travel design (commonly referred to as “second-generation leaf spring”), and FES-301E the lower-profile type (commonly referred to as “third-generation leaf spring”).

FES-301 is a development of FES-300 sheet keyboard switches. The sheet keyboards were introduced in the Fujitsu journal in November 1979. The Fujitsu Scientific & Technical Journal covered both the sheet and “typewriter” keyboards in September 1980, based on a manuscript received in March 1980. The series names of the switches were not given in either article, but a diagram in the Fujitsu journal in June 1985 names the two series and appears to indicate that FES-301 followed FES-300.

FES-301 is given as the switch type for FKB 2831 Series and FKB 3140 Series in Electronic Design’s Gold Book, Volume 2 1987, based on what little information can be observed on Google Books.


The contact assembly is virtually identical to that of FES-300. The significant difference is that the actuator leaf spring is significantly longer, providing much higher leverage. This may be what accounts for the difference in operating force between the two types. The need for high leverage led to two different approaches. The fully-discrete FES-360 switches used a second leaf spring embedded into the plunger. Keyboards with FES-301 switches simply offset the plungers further so that they are still above the end of the longer leaf spring.

The structure of the original FES-301–based keyboard design is roughly as follows (production keyboards appear to have deviated from the drawing in Fujitu’s utility model):

FES-301E–based keyboards follow the same principle, but have a lower-profile plunger assembly.

A Victor 108816-44 keyboard has been found with plungers similar to those of FES-370 and “Peerless” switches, and a case almost identical to that of FKB4700 Series.


Confusingly, FKB3000 keypads offer a choice of FES-301S and FES-310, where FES-301S appears to be a derivative of the low-profile FES-300 sheet keyboard switches. The reason for putting sheet keyboard switches into FES-301 series remains unexplained.


FES-301E switches are the DIN-compliant revision of FES-301. They are effectively the same design but reduced in profile. The only written mention discovered to date of DIN compliance is in the FKB2500 Series datasheet, but Fujitsu separately provided the name of the series in 2020 and explained that “E” denotes “ergonomics”.

Unlike with FES-360, these are documented to both linear and snap action. The plunger assemblies are identical to that depicted for integrated membrane leaf spring.



The material from the Fujitsu Scientific & Technical Journal and the Fujitsu journal is presented here by kind permission of Fujitsu. The Japanese material was originally obtained by 聖人 (Kiyoto) with whom this research was conducted.