instance has an external diameter of 0 625 34 and a height or thickness of 0 125 34 this diameter in other words is substantially the same as the diameter of the stem receiving chamber 16 or slightly greater than the diameter of the lower portion 46 of the stem 11 the washer 67 is secured to the surface 50 of the stem 11 by means of a machine screw 68 which extends through the hole 69 in the washer and is threaded into the threaded axial bore 66 of the element 63 it may be noted at this point that the portion of the stem of the screw 68 immediately above the head of the screw and for a distance equivalent to the thickness of the washer 67 is left unthreaded for a reason to be presently explained since the washer is of a diameter greater than the diameter of the upper end of the conical valve seat 21 the washer cannot enter this valve seat when the valve is closed but instead the washer seats on the flat upwardly facing bottom 17 of the valve body to thereby effectively close the valve the function of the ribs 44 and 45 is to provide a positive stop for the bonnet 12 when the valve is being closed to prevent over tightening of the bonnet and thus prevent breakage of the bonnet these ribs also serve to strengthen the portion 15 of the body 10 the disposition of the o ring 13 is such that it may be replaced when the valve is in the closed position moreover the.