Speedfit Spreader Plates for I Beam Joists 165mm x 1000mm Spreader Plates 165 x 1000mm can be used with traditional and TJI joists. They are fixed to the underside of the floor using staples or screws. Speedfit Pipe is fixed in the grooves of the plates. When the plates and pipework have been installed, insulation is placed in the void below the plates to minimise downward heatloss.