The 450mm Large Inspection Chamber Riser & Sealing Ring means that you can extended the height of a large inspection by 235mm to a maximum height of 1200mm with the standard frame & cover & upto 3000mm using a 350mm reduced access frame & cover. The riser can also be cut down to heights of 65mm 115mm & 117mm. The product is supplied with an integral rubber ring which forms the seal between the risers.