or jacking plate 56 is arranged between the frame 50 and the liner 52 the lugs 54 of the liner 52 are arranged for operative engagement with the jacking plate 56 more particularly the jacking plate 56 defines a plurality of recesses or depressions 62 into which the lugs 54 of the liner 52 are positionable for correctly locating the liner 52 relative to the jacking plate 56 the jacking plate 56 further defines a plurality of clearance cut outs or recesses 60 on its inner diameter the clearance recesses 60 are formed through the thickness of the jacking plate 56 and are wider than the lugs 54 of the liner 52 to enable the lugs 54 to pass within the clearance recesses 60 as will be described below in this embodiment the clearance recesses 60 are spaced equidistantly about the inner diameter of the jacking plate 56 and the locating recesses 62 are provided between the clearance recesses 60 in some embodiments the locating recesses 62 may have a tapered surface configured such that relative rotation of the liner 52 with respect to the frame 50 causes the liner 52 to tighten its engagement with the frame 50 fig8 to 11 show the steps in assembling the liner 52 on the frame 50 as can be seen in fig8 arcuate jack strips 64 three of which are visible in fig8 are mounted on an upper surface of the frame 50 e g adjacent the rim of the central opening in the frame 50 the jacking plate 56 is then placed on top of the jack plates 64 the liner 52 is arranged below the frame 50 e g as.