Abstract: A multi-component polymer rubber comprising (A) 15 to 60 mole % of an .alpha.,.beta.-unsaturated nitrile, (B) 10 to 75 mole % of a conjugated diene, and (C) 2 to 55 mole % of a fluoroalkyl acrylate or methacrylate or a fluorine-containing .alpha.-olefin, and having a glass transition temperature (T.sub.g) of -50.degree. C. to -20.degree. C., the percentages of the components (A), (B) and (C) being based on the total sum of moles of the components (A), (B) and (C). Said multi-component polymer rubber is excellent in sour gasoline resistance and alcohol-containing gasoline resistance.

Abstract: A curved blade rotor for a radial inflow turbo supercharger which is made of ceramic material and having a plurality of curved blades each with a curved outer edge. The surface roughness of the curved outer edge is 0.8S to 2S wherein "S" indicates surface roughness according to Japanese Industrial Standard B 0601.

Abstract: A prechamber cup for an internal combustion engine which is made of ceramic material and designed to have a sintered and surface finished exterior wall which is to be fit in a cylinder head, a sintered and surface finished passage portion through which a gas is passed and a sintered interior wall forming cup-shaped portion.

Abstract: A rotor-shaft assembly comprising a ceramic turbine rotor, a metal shaft and a metal connector disposed between the rotor and the shaft. The metal connector is fixed to the rotor by some suitable means and coupled with the metal shaft by mutual engagement of teeth provided at the ends of the connector and the shaft.