THE PILOT-IN-COMMAND TOUCHED DOWN ON THE GRAVEL RUNWAY AND BEGAN TO APPLY BRAKES. THE AIRPLANE BEGAN TO VEER TO THE LEFT AND THE PILOT RELEASED THE BRAKES AND USED ASYMMETRIC POWER AND BRAKING, BUT THE AIRPLANE STILL LEFT THE RUNWAY ABOUT MIDWAY DOWN THE RUNWAY. SUBSEQUENT EXAMINATION REVEALED THAT A SMALL WASHER PLACED BENEATH THE BOLT HEAD, WHICH HOLDS THE UPPER AND LOWER SCISSORS ASSEMBLY TOGETHER, HAD PULLED THROUGH ON THE LEFT MAIN GEAR ALLOWING THE LOWER HALF OF THE MAIN GEAR TO PIVOT FREELY.