A spark discharge igniter for gas turbine engines and the like. The igniter includes a tubular metal shell (10) (12) (14) and a relatively long ceramic insulator (16) inserted in the shell and rigidly secured (14) (22) to the shell near one end thereof. A metal collar (40) is fitted tightly between the insulator and shell at the end opposite the rigidly secured end. The collar is initially in the form of a split ring (40') installed on the insulator prior to assembly of the insulator into the shell. The ring is extruded into the tightly fitting collar in the course of inserting the insulator into the shell.