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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.

Symbol Year range Moniker
1966–67 Bell
1968 Hatchet (or selfie-stick megaphone)
1969–70 Star
1970 Clover (or suit of clubs)
Crown (as drawn by an alien following an interstellar telephone call describing such an object)

Known examples

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
11SM3 2-64 eBay 1
Bell Bell 7A1H-X17 6649 Flickr 2
Bell Hatchet 7A1H-X18 6651 Flickr 2
Bell Plus 7A1H-X27 6738 Flickr 1
7A1H-X4 6752 Flickr 1
Hatchet Heart 7A1HA 6832 Flickr 1
11SM3 eBay 1
Hatchet Crown 11SM3 eBay 1
Hatchet Crown 7A1H-X34 6845 Alfa-Inc
Star Square 7A1M-X1 6909 Alfa-Inc
Star Plus 7A1H-X39 6918
7A1CA 6947 Deskthority 1
Star Star 7A1HS 6949 Deskthority 1
7A1MT × 2 6950 Flickr 3
Star Clover 7A1MT × 3 7001 Flickr 3
Star Circle 11SM3 eBay 1
Clover Plus 7A1H-X17 7019 Flickr 2
Clover Diamond 7A1MS 7030 Deskthority 2
Clover Heart 7A1M-X14 7035 Deskthority 3
Clover Triangle 11SM3 eBay 1


  1. Auction listing of 24 Micro Switch 11SM3 switches (eBay 1)
  2. Burroughs D8585 keyboard (Flickr 1)
  3. Mohawk Data Sciences keyboard (Flickr 2)
  4. Potter Instrument KDR/KB 3100A (Flickr 3)
  5. Unidentified keyboard (Deskthority 1)
  6. Micro Switch 57RW1-2 (Deskthority 2)
  7. Micro Switch 53RW4-1 (Deskthority 3)
  8. Honeywell parts (Alfa-Inc)