Oak Series 415
Oak Series 415 is an extremely low-profile switch targeted towards desktop calculators. It was described and depicted in Electronic Design magazine in 1972 [ED1972-FOK], where it is cited as being only 0.415″ tall including the keycap. It is reported as having been recently introduced at the time of writing. Cost was given as 20 cents per switch in quantities of one million; for the depicted 16-station keypad, you would need to sell 62,500 units to consume that million-switch order. The design is covered in US patent 3916131, filed in 1974 with priority to a 1972 application.
It appears that the keycap is the plunger and thus part of the switch. This is in contrast to Alps “ultra low profile” where the keycap and plunger remain separate.
The following photographs were provided by Deepak Kandepet:
All material was scanned by Bitsavers unless otherwise noted.