Abstract: A blind fastener assembly for securing together panels or sheets of material which may have the same or different hardness and thickness and also for attaching articles to panels or walls of relatively soft material. The assembly includes a hollow rivet body having a fixed head portion at one end and longitudinally separable and spreadable sectors formed by axial slots at the opposite end of the rivet body. An elongated pin located within an axial cavity of the rivet has an enlarged tapered end portion. Between the pin end portion and the opposite end of the rivet body is a deformable sleeve member adapted to bear against the inner end of the rivet. Axial pulling force on the pin causes its tapered end portion to compress and deform the sleeve against the inner slotted end of the rivet body and ultimately causes its longitudinal sectors to spread apart.