permitting a degree of flexibility of the washer 63 a plurality of hemispherical nibs 64b are integrally formed on the bottom annular face of washer 64 the overall thickness of the washer 64 including the nibs 64b conforms to the actual depth of chamber 63 and as seen in fig3 the lower element 62 acts as a retainer to the washer 64 with the components assembled the outer diameter of washer 64 is slightly less than the inside diameter of the crown 61a with reference to fig3 and 10 the threaded coupling 80 comprises an upper cylindrical head 81 the outer circumferential surface of which is threaded to mate with the threaded surface 22a and an externally threaded nipple 82 that is screwed into a selected one of a plurality of threaded bores formed in the conduit arm 12 disposed between the head 81 and the nipple 82 is a square shank 83 which permits the use of a wrench in installing the sprinkler head 16 a large cylindrical bore 84 is formed in the threaded coupling 80 communicating with an axial bore 85 that leads upward from the threaded nipple 82 and receives water from the conduit arm 12 as best shown in fig3 the threaded coupling 80 is sized to urge the water jet means 60 upward against the annular flange 22b to effect a watertight seal the threaded coupling 80 as well as the top and bottom elements 61 62 are also integrally molded from plastic material preferably an acetyl copolymer thus with the exception of the washer 64 which is formed from a resilient.