Abstract: An improved, easily disconnectable coupling between a spring-loaded piston and a socket-type sleeve member adapted to receive such piston in a high-pressure radial piston pump is described. The piston terminates at a rear end thereof in an enlarged spherical section that defines a volume smaller than a hemisphere. The socket member includes a spherical recess that receives the spherical section of the piston, and a surrounding edge region that is crimped inwardly at diametrically opposite portions to define a plane of oscillation of the sleeve member with respect to the piston and to capture the spherical member in the sleeve. In order to retain the coupling parts in operative association with each other, an external abutment ring is pressed over the piston adjacent the spherical section, such abutment ring extending radially outward to contact the front end of the sleeve member when the latter has oscillated through a limited predetermined angle with respect to the piston.