We sell Datcon, Stewart Warner, ISSPRO, and VDO temperature gauges for HD equipment. Our water temperature gauges are 2" inch in diameter, which is the standard hole size for aftermarket fuel, volt, pressure, amp and temperature gauges (speedometers and tachometers are typically 3 3/8"). Many of these gauges are lighted, meaning they have a light bulb built in. The bezel is the metal ring around the edge of the gauge, typically in black or chrome. Oil temperature gauges are an important part of your instrument panel cluster. The oil temperature is a better indicator of the engine stress conditions than water temp. The oil temp comes up a lot slower, but will react to hard driving/easy driving conditions much more so than the water temp will.