Kronos 2" Hourmeter (10,000 Hrs) (12-32 VDC). 2" - Hole size: 2.0625" (53mm). Hourmeter operates by applying battery voltage across the gauges's register motor to ground. The register increments increase when the key switch in on. Route power through a normally open Oil Pressure switch to count "engine running" hours.. Benefits:. 0-10,000 Hours. Engine Running only