Abstract: A spacer formed of a relatively rigid frame is slidably adjustably mounted on and extends between a pair of horizontally spaced vertically extending ribs of electrostatic precipitator plates to maintain the plates in a predetermined horizontal spaced relationship. The frame preferably is formed by one or two rectangular-shaped frame members having U-shaped hooks attached thereto. The hooks are either attached directly to the plate ribs to frictionally slidably mount the frame between the spaced plates, or connect the two plates together with the plate ribs being clamped therebetween. The frame members and U-shaped hooks preferably are formed of round metal bars. The frame members are mounted on the ribs either at the top or bottom of the precipitator plates and then slidably moved along the ribs until positioned at the desired vertical location.