This is an NOS 1964 Ford Manual Transmission Snap Ring with part number C4AZ-7064-B / C4AZ7064B

Found the following info from Auto gear engineering

Mainshaft 1st/2nd Synchronizer Snap Ring

TREMEC 5 Speed: TR3550, TKO-500, TKO-600

I have 5 available, the package is not included until the last one is sold. 

Please use part numbers and picture to verify application. This may fit other makes and models not listed above. Please check your application. This NOS part is in excellent condition from dry storage.  Please email with any questions.