Thanks for all of the suggestions last week about using a cordless impact driver for 5/16 grain bin bolts. Menards had a special on Hitachi 18 volt impact drivers. The tool, two lithium batteries, and charger for around $100. Better than anything I could find on ebay. Comes with a full factory lifetime warranty covering materials and workmanship (whatever that means). Easily has way more power than required to torque down the bolts. Seems to have about a much power as my corded impact wrench. Easy to use all day lifting it up and down. Was thinking about getting a 3/8 or 1/2 inch square drive, but this 1/4 inch hex drive will have more uses driving screws after the bin is built.