McGuire Glossary of Fastener Terminology

U - 7 terms

UHMW (PLASTICS) - While ultrahigh-molecular-weight polyethylene retains the inherent qualities of low-density polyethylene, its increased toughness allows its use in a wide variety of rugged applications. It is commonly employed to provide rollers, cams, impellers and bumper guards. Because of its high lubricity, it is also used to coat conveyer-belts, ramps and hoppers. UHMW's imperviousness to attack by steam and chemicals, and its continued good performance at low temperatures, has also enabled it to gain FDA approval for a variety of applications within the food and drug industries.

ULTEM(R) (PLASTICS) - Unreinforced ULTEM(R) (polyetherimide) keeps its hardness, and mechanical properties from -40F up to temperatures of 356F. It is radiation-resistant, microwave transparent and is naturally flame-resistant. Reinforced grades have even higher mechanical strength. Because ot its unequalled properties, ULTEM(R) is the ideal replacement for steel and other metals. It also has a wide range of electronic and medical applications.

ULTIMATE THREAD STRENGTH - The force required to cause significant yielding or fracture of an insert when the head is supported and a load is applied to the threads in a pulling direction from the head side. It is equivalent to the insert being over-installed to failure. The difference between ultimate thread strength and installation load is significant in that it represents the size of the force window needed for tools that install to a constant force. Spin-spin tools install to a constant torque, but for consistent thread friction conditions, they in fact install to a constant force.

UNDERCUT - The triangular or rectangular shaped groove applied to the shank of a self-clinching fastener located between the displacer and the shank. The purpose of the undercut is to accept the panel material displaced by the displacer.

UNDERFILL - Primarily used in heading and forming work to donote a condition in which the work material did not competely fill the die cavity. Most common examples are on the head of type S nuts, and on step of studs.

UNTHREADED LENGTH - That portion of the axial length of a stud, at its head end, that is unthreaded.

UPSET - A term sometimes used as a verb to describe the act of creating a the bulb when installing a blind threaded fastener. It is commonly used in cold heading and solid riveting and has been applied to inserts because forming the bulb is similar to forming a fastener head by upsetting. In heading work the operation of signicantly increasing the diameter of the work by striking it from the end.