UNDER STEER – The tendency of the vehicle not to turn as much as the wheels are turned.

UNITIZED CONSTRUCTION – A type of automobile body and frame construction in which the frame and body parts are welded together to form a single unit.

UNSPRUNG WEIGHT – That part of the vehicle which is not supported on springs (the wheels and tyres for example). The vehicle weight moved by variations in the road surface.

UNIVERSAL JOINT – The part of the drive line assembly that allows for a change in angle of the drive line as the vehicle goes over bumps.

UNCONTROLLED COMBUSTION – is the instantaneous combustion of the fuel that got accumulated in the combustion chamber, at the end of the delay period.

UNIT INJECTOR – A combined fuel injection pump and fuel nozzle.

U–BOLT – An externally threaded fastener bent in the shape of the letter U and with both ends threaded.

U–CLAMP – A flat or square piece of metal bent or formed into the shape of the letter U and used for clamping work-pieces on a machine table.

UNIVERSAL CHUCK – Design of chuck in which the jaws are moved simultaneously by gear wheels, by a scroll or by a combination of both. Also called concentric chuck or self centering chuck.

UNIVERSAL INDEX CENTERS – A dividing head and foot stock with a set of change gears to gear the spindle of the index head to the index crank for differential indexing, and to gear the index head to the lead-screw of the table of a milling machine for helical milling.

UNIVERSAL VICE – A work holding device usually used on the milling machine which has either two or three swivel settings so that work-pieces may be set at any desired angle including compound angles.

UNIVERSAL GRINDER – Type of grinding machine having a wide range of application and specially suited to work that has to be ground at an unusual angle. Provided with a swivel table and headstock and a wheel head that can be rotated on its base.

UNIVERSAL MILLING MACHINE – Design of milling machine of the column and knee type, roughly similar in general design to plain milling machine (column and knee type), but usually of less robust construction and having additional features that widen its field of usefulness e.g., a worktable that swivels in a horizontal plane so that it is not restricted to two right angled motions.

U-BOLT – An externally threaded fastener bent in the shape of the letter U and with both ends threaded.

UNITIZED LOAD – A grouping of smaller shipments that are bound together to travel as a single larger unit, also called UNIT LOAD.

UPENDERS AND DUMPERS – Specialized machines used to unload materials handling carriers at a desired location.

ULTIMATE STRENGTH – Maximum conventional stress, tensile, compressive or shear that a material can withstand. The highest strength that a metal exhibits after it begins to deform plastically under load. Rupture of the material occurs either at the peak of its ultimate strength or at a point of further elongation and at a drop in stress load.

UPSETTING – Process of increasing the cross-sectional dimensions when forging, with consequent reduction in length. May be done manually or by machine.

UPSET FORGING – The process of increasing the cross-section of stock at the expense of its length.

UNCONSTRAINED KINEMATIC CHAIN – An arrangement of links wherein for a given motion of one of the links, each of the others is not constrained to move in a definite predictable manner.

UNIVERSAL JOINT – Joint used to connect intersecting shafts (e.g., Hooke or cardan joint).

UNIT DISTRIBUTOR – An ignition distributor, used by General Motors, that uses a magnetic pick up coil, and timer core instead of points and condenser. It has the ignition coil assembled in the distributor as a unit.

UPDRAFT CARBURETTOR – is the carburettor in which the air fuel mixture flows upward. This unit can be placed on the side of the engine.

UNDERFEED STOKER – One in which the fuel is fed upward from underneath.

UNDER EXPANDING NOZZLE – A nozzle which operates with a back pressure below the designed value of pressure at the exit of the nozzle.

UNIFIED BRAKE SYSTEM – A system that automatically coordinates the front and rear brake systems when the rider applies pressure to the brake pedal.

UNIT CONSTRUCTION – Engine design which has one crankcase to house gearbox, clutch, primary drive and engine.

UNIVERSAL JOINT – A flexible joint which allows changes in angle of drive shaft.

UNSPRUNG WEIGHT – The weight of the two wheeler components that are not supported on springs, includes the wheel assembly, fork sliders, rear shocks, a portion of the swing arm, the chain or shaft drive, one half of the spring and on some models, the front fender.

UNDER WELDING – Depositing less filler material than required.