all when the cap nut is tightened the fluid joint coupling for clamping the cap nut has a ring shaped groove formed on the contacting surface of the sleeve with the cap nut to rotatably hold the small spheres in the groove application_number US 80416285 A description this invention relates to a fluid joint coupling comprising tubular body formed with a threaded portion on the outer periphery of one end a tubular sleeve provided with a short ring shaped portion on the outer periphery of the end communicating with a through hole of the body at the threaded portion of the body a gasket between the body and the sleeve a cap nut engaged with the sleeve for engaging with the threaded portion of the body to rigidly clamp the body and the sleeve and a ring shaped groove formed on the contacting surface of the sleeve with the cap nut of the short ring shaped portion and a number of small spheres being rotatably held in the groove an embodiment of the present invention is described hereinafter with reference to the attached drawings in fig3 the fluid coupling shown comprises body 11 sleeve 12 and cap nut 13 the cap.