5 Speed transmission:

I have a couple 5th gear syncros with two brass syncro rings, one ring for the 5th gear position and one for the reverse.
I also, have this one (photo attached) that has a brass ring for 5th gear position and no brass syncro ring for the reverse position.
The syncro in the photo has a much heavier hub and brass syncro ring than the others. I don't know why a syncro ring is need for reverse.

Can anyone identify it? When was it used? On what models and years?

Looks like this one is much better and stronger that the others.

Attached Thumbnails

 

It's a newer design. Used on push clutch 5 speed gearboxes circa 2006 onwards. (in Australia, to my knowledge) May have appeared earlier in the USA market as you had EJ25 turbo engines before we did here. Very early WRX boxes had no brake on reverse gear and were difficult to select and often crunched on reverse selection. Circa 1996 Subaru revised the design to incorporate the reverse brake on the back of 5th gear. It applies a brake to the mainshaft as reverse is selected, it does not 'synchronise' reverse gear, it just slows the mainshaft to prevent crunching. I don't know why they have deleted the brake from newer versions, but the synchro and hub is definately revised and appears to be more robust. As always, use extreme care swapping parts between transmissions of differing eras, something will always catch you out.

Thanks for the information. I appreciate it.