Review on Spark Plug Index Shim by Allstar Performance ALL96506 by Bobby Posner

Thin steel lock washers. Two thickness sizes (0.2mm and 0.3mm); they correspond to the rotation of the plug for 10 minutes or 15 minutes. counterclockwise for each size you will use. (on a regular 12 hour dial). Torque the spark plug to 20-30 lb-ft to align the lock washer to a nice flat shape; Then add indexing discs to rotate counter-clockwise until you are where you want to index. (I've been indexing surebets since I was 24 and this was the easiest method in 49 years.)