| 摘要 |
A method of manufacturing a hollow spark plug body having a cylindrical central portion (28), a first end portion (10) of smaller circular radial cross-section and a second end portion () of non-circular radial cross-section, eg. hexagonal, and of smaller maximum diameter than the central portion by cold extruding the both end portions The second end portion is extruded in two stages, the first involving the formation of a recess in one end of a cylindrical blank, the second involving extrusion the blank between a die (19) and a mandrel (21) which moves with the blank during extrusion |
