of 18 lbs gal mud such flotation materials are commercailly available for example from emerson amp cuming inc normally the inside diameter of liner 48 is the same as the inside diameter of the last casing run and through which drilling operations are to be continued in fact standard sizes in casing tubing can be used effectively as a wear liner straps 59 are provided about the outer wall of the inserts attention is now directed to fig2 and 3 for means of holding the lightweight insert in the riser pipe at a depth or location along the riser 26 at which it is desired to have the bottom of the inserts there is provided a modified 34 j 34 slot arrangement 108 this can be quite similar to the locking slot arrangement 130 shown in fig9 and 10 a locking spider 124 is provided at the lower end of the insert 47 and is provided with four lugs 112 which are 90 u00b0 apart and can be similar to the locking lugs 132 shown in fig9 and 10 the locking spider 124 is connected to flotation unit 47 by pipe means 114 means will now be discussed as to methods for holding weight 116 to pull the insert 47 down and also means for removing the weight 116 this includes pipe 118 hung inside insert liner 114 and extends downwardly through the spider arm 124 outwardly biased arms 119 pivoted about pivot 120 on pipe 118 are provided so that when they reach cavity 121 within spider 110 they will expand and engage the lower shoulder 122 of cavity 121 at this point the downward force of the weight of weight bar 116 is applied through spider 124 to insert 47 pulling.