Backlit dials provide unmatched nighttime readability Impact-resistant double-wall lenses prevent fogging and curved to minimize daylight reflections Corrosion proof body and bezelStepper-motor technology and air core movements for reliability and smooth pointer movementsSpin-Lok™ mounts for fast,secure installation, reduced installation depthSpeedometer and Tachometer are 3-3/8" (85mm) in diameter. All other gauges listed here are 2-1/16" (52mm) diameter