NOVELTY - The plug (1) has center electrode (5) is inserted into axial hole (4) at front end. A tubular metallic shell (3) is provided around insulator (2). The proximal end portion of ground electrode (27) is fixed to front end portion (26) of metallic shell. A tip (32) is bonded to distal end portion of ground electrode such that gap (33) is formed between tip and front end portion of center electrode. The tip is formed of metallic material containing specific amount of nickel and having specific range of Vickers hardness.    USE - Spark plug for internal combustion engine. Can also be used in fuel cell reformer.    ADVANTAGE - Since the tip is formed of metallic material containing specific amount of nickel as main component, the production cost of spark plug is reduced. The tip has the specific range of hardness, so that the strain of crystal grains in the metallic material is suppressed, the thermal conductivity and the erosion resistance of the tip can be improved. Thus the ignition performance can be improved by providing the tip. The residual stress is applied to surface of the tip and the surface forming gap, so that occurrence of breakage at the discharge surface is reduced, thus rapid increase in the size of the gap due to breakage at the discharge surface can be prevented, increase in discharge voltage can be suppressed, rapid erosion of the tip can be suppressed and the spark discharge at a portion other than the gap can be prevented. The productivity can be improved by preventing the breakage of supporting jig. An annular sheet packing intervenes between the stepped portion of the insulator and the stepped portion of the metallic shell, so that gas tightness of combustion chamber is retained and leakage of fuel gas can be prevented.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for method for producing spark plug.    DESCRIPTION OF DRAWING(S) - The drawing shows a partial sectional view of spark plug.    Spark plug (1)    Insulator (2)    Metallic shell (3)    Axial hole (4)    Center electrode (5)    Front end portion of metallic shell (26)    Ground electrode (27)    Tip (32)    Gap (33)