I'm seeing a lot of older corn heads that have marred check-plugs in the top of their row-unit gear cases. Those are the plugs you remove to check the level of gear lube in each row's gearcase. The plugs often have square, recessed holes--or allen head holes--in their tops. Most folks use a 1/2-inch or 3/8-inch socket wrench to remove the plugs.
That's fine in theory, or with new corn heads, but those plugs can be practically welded into older corn heads. All the marred, chewed-up, stripped out plugs I'm seeing suggest that guys are either using a standard 1/2- or 3/8-inch breaker bar with a cheater handle, or they're using an air-powered impact wrench in an attempt to break those plugs loose. And apparently, they're stripping out about 1/3 of the plugs on an average cornhead.
The problem is that breaker bars and air impact wrenches provide extra rotational power, but those frozen plugs need rotational power AND downward force to break them loose. That's where an impact screwdriver can save the day. Impact drivers are stout little tools with a very stiff internal spring associated with internal cams. You give the top of the driver a hard whack, and the spring and cams convert the hammer blow into simultaneous rotational force and downward impact. Perfect for cracking loose stubborn, frozen bolts. Or plugs that have been mangled by breaker bars with cheater handles, or air-powered impact wrenches.