Abstract: An improved deformable locking fastener system comprises a fastener, a deformable collar and a dedicated installation tool. The fastener has a threaded exterior defining a plurality of axial flutes which are configured to prevent of the collar from prematurely captivating the fastener during installation. The collar comprises a cylindrical forward portion, a central portion having an elliptical cross-sectional shape and a rearward portion having an elliptical cross-sectional shape. The collar portions have axial heights selected to maximize the strength of the collar and to minimize the weight of the collar. The installation tool contacts the collar along driving ridges which reduces the radial compression of the collar and increases the tangential driving force turning the collar during installation.