A spark plug includes a metal shell, an insulator coaxially disposed within the metal shell, and a center electrode coaxially disposed in the insulator.

The invention relates to a sparking plug comprising a metallic housing (10), an isolator (11) which is accomodated in the housing (10) and a rod-shaped inner conductor arrangement which is arranged in said isolator (11).

The metal shell has a substantially cylindrical base portion, and the base portion has a lower surface with a recess formed therein.

The recess in the lower surface of the metal shell is preferred to be provided as an annular groove extending therearound.

In spark plugs, the metal housing (63) is earthed (5) to the vehicle via the cylinder head (71) of the engine (7).

A spark plug assembly includes an insulator having an upper shoulder and a lower shoulder and a metal annular outer shell having an outer surface and a cavity bounded by an inner surface.

A foamable copolymer based coupling (27, 29) is provided for securely affixing a light emitting glass lamp (3) in a metal base (1) to form a lamp assembly.

The metal cap attachment part (63) has a cylindrical shape and has a screw peak (61) protruding on the outer circumference face which is capable of screwing together with the screw groove (51a).