extending groove 32 in the vertically outermost side of each lip member 20 such groove 32 extends chordally with respect to the subtended arc of the die lip 21 and defines or forms a thin flexible leg 33 and foot 34 of the lip member 20 the flexible leg 33 extends axially inwardly from the die lip 21 whereas the foot 34 extends vertically outwardly from the end of the leg it is the foot 34 which is clamped to the die body 29 by the aforementioned retainer bar such foot being urged into sealing and sliding engagement at full width toe and heal projections or seals 35 and 36 with an accurately machined die body end face 37 accordingly the toe and heel projections provide two spaced continuous high pressure seals between the die lip member and die body face 37 while permitting vertical adjustment of the die lip or more accurately vertical adjustment of the foot 34 of the die lip member as both die lip members 20 are similarly mounted to the die body vertical adjustment of one or both die lip members effects corresponding adjustment of the spacing or gap between the feet thereof as should be evident such adjustment of the spacing between the feet effects a certain related adjustment of the spacing or gap between the chordal or arc ends of the die lips 21 with the foot 34 of the die lip member 20 securely and sealingly.