2-1/2" Dia. outlet. Runs smooth, quiet and variable speed works fine. The switch has a bracket on the back for clamping to a round forge leg. It does not look like it has ever been used byt someone may have made it up out of new components. The return address on the old mailing label is Middleton, WI. I don't know if this could have been Centaur Forge (blacksmith supplies). Clean and very good condition. Please let the pictures help with the description and condition. Please view my other auctions for more blacksmith tools, hammers and anvils.