Truck Rack Accessories - For Holman PROII Full Size Truck Rack Only. The Holman Clamp Cross Bar Can be positioned anywhere along the length of the rack to provide additional support where needed. This Clamp Cross Bar can be easily installed or removed to accommodate taller loads. This cross bar is constructed using 2" round tubing to accommodate heavy loads. All Holman items are zinc primed and covered with marine grade powder coat to provide excellent corrosion resistance.