Overview

Synchro is two cones pressed together until the two shafts run the same speed:

Each gear has a syncho face (external cone) machined with it

The hub is spring loaded so when you move the shifter partway, it presses the baulk ring (internal cone part) against the gear.

When they have slow down to the same speed, the shifter will move all the way in. It happens very quickly, unless the synchros are worn and not working well.

Synchro is basically:

Coupling with hub
Baulk rings and gear faces

Coupling with hub. Left: assembled. Right: not assembled
photo

Each synchro set services two gears (arrows). Center arrow points to the Coupling Sleeve
photo

The Coupling Sleeve is what the shifter moves.

The hub is keyed to the mainshaft, so the sleeve rotates constantly in the Shift ForK while the car is moving.

The spring lets the hub move side-to-side inside the Coupling Sleeve, but not move too far. On this one there is a total of about 1/4" (5mm) total movement possible.

56-Series Transmission

FS5C56A 5-speed has very different synchros from other A-series transmissions. It has "C" type synchros (the "C" in FS5C56A) which are very different

4-speed: W56 'W' Warner (Borg Warner) type syncromesh 
5-speed: C56 'C' Cone-Type (Porsche-type) synchromesh
See Transmission Gear Part Numbers

4-speed F4W56L, F4W56A
32604-H9000 RING-BAULK (4) > 32604-H1000 <> 32604-H1010
32609-18000 INSERT-SHIFTING (6)
32603-18000 SPRING-SYNCHRONIZER (4)
32601-18000 HUB-SYNCHRONIZER (2)
32606-18000 SLEEVE-COUPLING (2)

5-SPEED FS5C56A
32601-H7200 HUB-SYNCHRONIZER (2)
32606-H7200 SLEEVE-coupling (2)
32611-H7200 RING-synchro
32612-H7200 BLOCK-thrust
32613-H7200 BLOCK-anchor
32614-H7200 BAND-brake 22 (2)
32616-H7200 CIRCLIP

Also see 56-Series_Transmission_Parts#Synchros.

60-Series Transmission

32604-H9000 RING-BAULK
* F4W56A 4-speed light duty (4)
* F4W60L 4-speed heavy duty (4)
* FS5W60L 5-speed early (5)
32604-H9700 RING-BAULK
* FS5W60A 5-speed late (5)

FS5W60L 5-Speed (1979 B310)
32606-18000 SLEEVE-COUPLING 4th-5th, 2nd-3rd
32604-H9000 RING-BAULK 5
32258-H9001 HUB-SYNCHRONIZER 1ST & REVERSE $133.92 USD
  32602-32200 SPRING-SYNCHRONIZER 1ST 3
  32608-H9000 INSERT-SHIFTING 3
  32234-H9000 RETAINER-SHIFTING INSERT
32601-H9001 HUB-SYNCHRONIZER 2ND & 3RD
  32603-18000 SPRING-SYNCHRONIZER 2
  32609-18000 INSERT-SHIFTING 3
32601-H9000 HUB-SYNCHRONIZER 4TH & 5TH
  32603-18000 SPRING-SYNCHRONIZER 2 
  32609-18000 INSERT-SHIFTING 3

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