Make objects interacting with a given object of the same material, or material with identical properties.
EXAMPLE:
The cores of permanent casting moulds have almost the same coefficient of thermal expansion as the cast parts. This way, thermal stresses within the castings are avoided.
The glass and the foil of laminated glass sheets have the same optical refractive index.
The transport of small steel balls in a pipe entails an increased wear on the inside of the pipe bends. To minimize the wear, a layer of these balls, held in place by a permanent magnet, is positioned between the pipe wall and the flow of balls. By doing so, the flowing balls no longer collide with the pipe wall, but with the captive layer of balls.
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Inventive Principles 