Micro Switch symbolic date codes
Some Micro Switch parts are marked with pairs of symbols. So far they are known from some Series KB reed switches and some SM Series microswitches. Inspection shows that they are clearly chronological. The charts for KB series reed switches indicate that switches are to be marked with the “date code symbols of reed basic …”, which implies that the symbols on KB switches indicate the manufacture date of the internal reed capsule. No mention is made in the charts of a numerical date code, which is always present even when the symbols are omitted.
Two observations serve to corroborate this theory. The imperfect correspondence between the symbols and date codes fits with the reeds being manufactured first. The lack of symbols on 7A1CA (mechanical) and 7A1H-X4 (dummy switch) would be correct.
Eleven symbols are known. There may be others; some switches in the 11SM3 auction listing have symbols that are too hard to make out but that do not appear to be any of the ten known symbols. The approximate year ranges (based on the examples shown further down) are given for those symbols that appear on the left-hand side.
|1968||Hatchet (or selfie-stick megaphone)|
|1970||Clover (or suit of clubs)|
|Crown (as drawn by an alien following an interstellar telephone call describing such an object)|
The following symbol codes have been observed; they are arranged in chronological order by date of manufacture, and parts with no symbol code—where found alongside parts that do have symbol codes—are arranged together by the first symbol.
|Symbol pair||Part||Date code||Reference|
|7A1MT × 2||6950||Flickr 3|
|7A1MT × 3||7001||Flickr 3|