I.c.engine spark plug

The angle mu of the portions of the earth electrodes 5 bent towards the centre electrode 3 is between 10 and 60 DEG . The spark gap FB1 is greater than the gap (a, Fig. 1) between the electrode 5 and the most adjacent corner of the insulator 2 and less than the path FB2 from the electrode 3 over the insulator surface to the electrode 5. The adjacent corner of the insulator and the tip of the centre electrode may be chamfered (Figs. 4 to 6).