Overview

Synchro is basically:

Coupling with hub
Baulk rings and gear faces

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

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

The Coupling Sleeve is what the shifter moves.

56-Series Transmission

4-speed and 5-speed synchronizers are very different
See 56-Series_Transmission_Parts#Synchros

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

5-SPEED
32601-H7200 HUB-SYNCHRONIZER (2)
32606-H7200 SLEEVE-coupling (2)

60-Series Transmission

B310 with FS5W60L 5-Speed shows this:

Synchro Hub - 1st & Rev
Synchro Hub - 2nd & 3rd
Synchro Hub - 4th & 5th

For the 4th-5th gear, or 2nd-3rd the coupling is the same part number:

32606-18000 SLEEVE-COUPLING

For the Synchro Hub inside the coupling:

32258-H9001 HUB-SYNCHRONIZER 1ST & REVERSE $133.92 USD
32601-H9001 HUB-SYNCHRONIZER 2ND & 3RD
32601-H9000 HUB-SYNCHRONIZER 4TH & 5TH

4-speed and 5-speed synchronizers

FS5W60L
32604-H9000 RING-BAULK 4 
32603-18000 RING-SYNCHRONIZER 4 
32601-H9001 HUB SYNCHRONIZER-2ND & 3RD 1
32609-18000 INSERT-SHIFTING 6

32602-32200 SPRING-SHIFTING INSERT (SYNCHRONIZER INSERT) 3
*  unique to F5W60L 
32608-H9000 INSERT-SHIFTING 9 
32258-H9001 HUB SYNCHRONIZER-1ST & REVERSE 1

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