Terms starting with U

A distribution where values near the limits are most likely, used for cycling effects such as RF mismatch or room temperature.

Upper control limit: the top boundary on a control chart, paired with the lower control limit (LCL) below the centerline.

Imitation of an impact wrench, meaning tightened by impact until it sounded done rather than to a torque spec. Shop talk

Unified Glare Rating: a calculated index of discomfort glare from interior luminaires, where lower numbers mean less glare.

Ultra-high vacuum: pressures below about 10⁻⁷ mbar, reached only with baked, metal-sealed systems.

The lowest pressure a pump can reach on a sealed, clean test dome, as stated on its data sheet.

Bonding or laminating by vibrating a horn at ultrasonic frequency against a patterned anvil roll to melt fibers locally.

Greasing a bearing while listening with an ultrasonic detector and stopping when the noise level drops.

Unified National Coarse: the standard coarse inch thread series, such as 1/4-20, 3/8-16 and 1/2-13.

A number that states how much doubt surrounds a measured value, as a standard deviation or as a stated interval.

A table listing every uncertainty source in a measurement with its size, distribution, divisor and contribution to the total.

A film that did not get enough time at temperature to crosslink fully, so it looks fine but performs poorly.

A notch cut into the base of small-pinion teeth when the generating tool removes part of the working involute.

Digging out soft or unsuitable subgrade below grade and replacing it with better fill. Shop talk

A recess deliberately machined below finished size so the coating can fill it to full thickness.

A notch the arc melts into the base metal beside the weld toe that the weld metal never fills back in.

Unified National Fine: the inch thread series with more threads per inch, such as 1/4-28, 3/8-24 and 1/2-20.

Geogrid with its strength concentrated in one direction, used to reinforce walls and steep slopes.

Stepped cone drill bit that cuts several hole sizes in sheet metal boxes and panels, named for its brand. Shop talk

Corrosion spread evenly over a whole surface, thinning the metal at a fairly predictable rate.

How evenly light is spread over an area, expressed as a ratio such as minimum to average or maximum to minimum.

A three-piece threaded fitting that lets a section of pipe or a valve be disconnected without turning the pipe.

Brand name used for metal strut channel, the slotted steel channel bolted together into racks and supports. Shop talk

A train carrying a single commodity in identical cars from one origin to one destination.

Lab shorthand for particles that hit the surface without fully melting and kept their round shape. Shop talk

Shop joke for a part or material that is impossible or absurdly expensive to get. Shop talk

Unified National Round root: an external inch thread with a required rounded root, for better fatigue life.

Said of a chamber that has been vented to atmospheric pressure and is open or ready to open. Shop talk

Ultra Physical Contact: a domed singlemode connector polish with no angle, color-coded blue.

Welding vertically from the bottom up, which gives deeper fusion and more fill per pass. Shop talk

To thicken part of a wire or bar by squeezing it along its length, the basic move that forms a fastener head.

Hydroxyl polyester powder cured with a blocked isocyanate, known for smooth, thin films.

Ultrasonic testing: finding internal flaws by sending high-frequency sound into a weld and reading echoes.

Unit under test, the instrument being calibrated or tested, as opposed to the standard used to check it.

Setting an instrument's ultraviolet content so fluorescent samples read as they would under the specified illuminant.

An adhesive that cures in seconds when exposed to ultraviolet or visible light of the right wavelength.

Filter that blocks wavelengths below about 420 nm so a sample can be measured without its fluorescence.

How much strength a geosynthetic keeps after exposure to ultraviolet light in an accelerated weathering test.