Reflectors must be mounted not less than 24 inches nor more than 60 inches in height above the ground on every poletrailer and on trucks, buses, truck tractors, trailers, semi-trailers which are 80 or more inches in width or 30 feet or more in overall length. (p 15-3)
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It depends on how high the ceiling is.
Six inches
Above ground!
The average height of a handrail is typically between 34 to 38 inches above the surface it is mounted on.
8 to 10 inches
6-12 inches above ground
I generally mount them so the spout is about 3 inches above the sink, but a lot depends on the design of faucet.
The top of the trailer hitch ball should be aprox 18 to 20 inches off the ground.
6-12 inches above ground and flat
18 inches is usually taken as a minimum. I see an fit lots of range hoods and most are mounted so the bottom is 20-21 inches above the cooking surface.