very aggravating for the seal assembly 20 to fall in the mud when the hammer union 10 is being assembled accordingly the seal 64 is selected so its external diameter is noticeably larger than the largest groove 26 so that when the insert 62 and seal 64 are placed in the groove 26 the seal assembly 60 is wedged in place by the seal 64 in other words the seal 64 wedges the seal assembly 60 in place before the seal 64 is compressed by the seal seat 46 of the nut end 16 to these ends the insert 62 comprises an annular metal member 66 the insert 62 might have separate grooves on its side and end but it is much preferred to provide a rabbit or groove 68 on an exterior edge facing the seal seat 46 and the groove 26 the groove 68 accordingly includes an annular face 70 parallel to the flow axis 48 and a annular shoulder or face 72 perpendicular to the flow axis 48 the groove 68 accordingly opens through the outside diameter of the insert 62 to face the thread end 12 and opens through the a rim or shoulder 74 to face the seal seat 46 the groove 68 is typically a small fraction of the cross sectional size of insert 60 a butt end 76 of the insert 62 abuts the groove 26.