Title: Spark plug
Application Number: 200610127726 Application Date: 2006.09.01
Publication Number: 1925241 Publication Date: 2007.03.07
Approval Pub. Date: Granted Pub. Date:
International Classifi-cation: H01T13/20
Applicant(s) Name: NGK Spark Plug Co. Address:
Inventor(s) Name:
Attorney & Agent: liuxin yu zhanghui hua
Abstract:
    A spark plug is provided with a metal shell and a ceramic insulator to support therein a center electrode. The ceramic insulator includes a front portion with a stepped outer surface, a middle portion, a rear portion and a shoulder portion defined between the middle and rear portions. A difference between the outer diameters of the middle and rear portions of the ceramic insulator is 1.8 mm or smaller. The metal shell includes a radially inward protrusion to retain thereon the stepped outer surface of the ceramic insulator and a rear end portion crimped onto the shoulder portion of the ceramic insulator. An inner circumferential surface of the crimped shell portion has a region held in contact with the insulator shoulder portion with a radially innermost point of the crimped shell portion being spaced radially apart from the ceramic insulator and axially apart from the insulator shoulder portion.
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