honing. A method of removing a very small amount of material from a metal surface by abrading the surface with a fine stone. Honing is used to produce a smooth finish on a surface, or to produce a sharp edge on a knife or chisel.
honing (cylinder wall treatment). Scratching the surface of the cylinder wall with an abrasive stone to produce a series of grooves of microscopic depth and uniform pattern. The honed pattern holds oil to lubricate the cylinder walls.
Hooke’s law. A basic law of physics that deals with the relationship between stress and strain. Hooke’s law explains that the strain within a material (the amount the material deforms) is directly proportional to the amount of stress that causes the deformation. This is true only until the material reaches its elastic limit.
When the stress that strains a material within its elastic limit is removed, the material will return to its original size and shape. But, if the material is strained beyond its elastic limit, it will not return to its original size and shape, but will be permanently deformed.
hook rule. A steel scale with a projection off of one end of the scale at the zero position. A hook rule is used to measure to the edge of a piece of material that has a radius on its edges.

hook spanner. A type of wrench used to turn a splined shaft. Some hook spanners have a hinged hook that allows them to be used on shafts of different diameters.
hopper. A funnel-shaped container with an opening in the top for loading and a smaller opening in the bottom for dumping. Hoppers are used to store the abrasive in an abrasive blaster. The abrasive is loaded in through the large opening, and it feeds out as needed through the small opening.
hopper-type oil tank (reciprocating engine oil tank). An oil tank, or reservoir, in which there is a hopper around the outlet from the tank. When oil dilution is being used, the diluted oil fills the hopper before the engine is shut down. Then, when the engine is started, the diluted oil is the first used. This diluted oil helps start the engine in cold weather. As soon as the oil begins to warm up, oil around the outside of the hopper feeds into the engine.
horizon. The line we see that forms an apparent boundary between the earth and sky.
horizontally opposed engine (reciprocating engine). A reciprocating engine in which the cylinders are arranged in two banks separated by 180°, with the cylinders and crankcase mounted in the aircraft so they are flat. The cylinders are staggered, with one bank slightly ahead of the other. Staggering the cylinders allows each piston to be connected to a separate throw of the crankshaft. Horizontally opposed engines are called flat engines.