A spacer is provided for maintaining the spacing between a pair of adjacent electrostatic precipitator plates having corona electrode wires positioned midway therebetween. The plates are of the type having a generally planar vertically extending surface spaced horizontally from and extending parallel with the planar surface of an adjacent plate. Vertically extending ribs are formed on the plates, the ribs projecting perpendicular from the planar surfaces inwardly toward the ribs on the adjacent plate. The spacer includes a pair of braces which extend horizontally between the adjacent pair of precipitator plates. The braces compressively engage the vertically extending ribs therebetween. Each of the braces is provided with a pair of plate engaging edges at opposite ends thereof and at least one angled edge. The angle between the contiguous plate engaging and angled edges is greater than about 110.degree., in order to facilitate mounting of the spacers. The spacer has a configuration which allows it to be easily moved into a desired vertical location and locked into final position without requiring a workman to enter into the space between precipitator plates, and without the need for overcoming high frictional clamping forces during placement.