When installing a ball on a hitch mount, can you tighten the ball down while the mount is inserted into the hitch itself? I know these ***** with a 1.25" shank require around 400 ft lbs of torque..

 

Yes. That is actually pretty common practice for those without a vice.

 

Even with a vice I can easily move my heavy bench

Yes go ahead and insert into the receiver and crank her down. Many shops will impact it on for you as well at no charge.

 

One thought is turn the draw bar sideways so you can put your weight on to the wrench (or pull up). May seam like a simple statement but you would be surprised by how many people I see trying to yank sideways to tighten the nut.