4 different switched can be found on TR2-4 (TR4A-6 used a switch external to the hydraulic system) However there is considerable confusion about what was fitted when, so all the variations are listed below so that you can be sure to order the correct part

13H2303 TR2-3 up to commission number TS13045 Lockheed 1/8" NTPF taper thread. Screw connections
C16062A TR2-3 up to commission number TS13045 Lockheed 1/8" NTPF taper thread. Lucar connections (not original). We have however taken this part off a TR4 CT13802 which had clearly never been in pieces before.
126845 TR3 after commission number TS13045 and TR4 Girling 3/8"x 24UNF thread. Screw connections
21B291 TR3 after commission number TS13045 and TR4 Girling 3/8"x 24UNF thread. Lucar connections.
The photograph shows the two thread types where the UNF threaded switch has a longer thread than the NTPF and it has the chamfered seat at the end whereas the NPTF version is shorter with a flat end and is visibly tapered.