The Jouplast 80/140mm Plastic Adjustable Decking Risers provide an innovative and effective way to ensure that you end up with a perfectly level deck. Simply lay a timber joist across a line of risers and attach to the head with a wood screw we recommend using wood screw product code 156547. Place a spirit level on top of the joist and then rotate each green nut to raise or lower the joist to set the perfect level. Up to 4 extensions can be used per riser to give an overall height increase of 380mm.