Abstract: An explosively-separable fastener that consists of two units held together in spring-loaded fashion by a hollow retaining bolt and adapted for mounting between two joined stages of a rocket. The rocket stages are connected by means of electrical contacts between the units and an umbilical line passed through the retaining bolt. An explosively-actuated cutter operable to sever the retaining bolt and the umbilical line threaded therethrough is mounted on a chamber disposed transversely to the retaining bolt. Upon actuation of the cutter, the hollow bolt and the umbilical line are severed releasing the spring-loaded assembly, thus also interrupting all electrical contacts between the two rocket stages.