the tank as needed to adjust the stop height of the blade and to set the upper limit of travel for use as an upstop the clamp is positioned at a level that prevents the blade form rising past the level of the headlamps of the vehicle if the blade blocked the headlamps it could produce a hazardous driving condition the upstop works by blocking the upward movement to the swing arm assembly 30 this occurs when the tubing pieces 32 and 33 on the swing arm assembly contact the clamp 71 clamp 71 simply blocks any further upward movement of the released assembly and therefore the blade the uplock device is used to ensure the safety of the vehicle when the blade is not in use typically most blades are held up by hydraulic or pneumatic pressure if the hydraulic system failed the blade would drop to the road bed if this occurs when the vehicle is in motion at highway speeds it could cause serious damage referring now to fig6 and 6a two different uplocks are disclosed the first is a manually operated device to operate the uplock the latch 73 is pivoted outward from the pedestal the swing arm assembly 30 is then raised unti the holding bar 36 is above the latch jaw 77 the latch is then pivoted back until the latch jaw 77 is under the holding bar the swing arm assembly 30 is then lowered until the holding bar is securely held by the latch 73 a second uplock is also disclosed this.