Synchronizer Ring

Check if the clutch gear teeth are damaged or broken.
Check internal surface for damage, wear and broken threads.

Fig 1: Checking Clutch Gear Teeth And Internal Surface Of Synchronizer Ring
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
Force the synchronizer ring toward the clutch gear and check clearance "A". If "A" is less than the limit, replace the synchronizer ring.
Minimum limit: 0.5 mm (0.020 inch)

Fig 2: Identifying Clearance Between Synchronizer Ring And Clutch Gear
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.