ac hd5
Usually around .120-.125 or roughly 1/8" longer than the standard measurement is worn out. That said if has 6" rails 6 1/8" is worn out, 6 and 1/4" would be 6 3/8" and so on. HD5 should be a 6 1/2" (or a little less) when new, if measure out to 6 5/8" or longer are worn out pin to bushing wear.