Allstar Spark Plug Index Shims 14mm Small O.D. ALL96506

Stackable shims index spark plugs at 30° intervals up to 360° properly positioning ground strap in cylinder head for increased power and clearance between spark plug and piston. Shims are intended for use with 14mm flat seat spark plugs only. Package of 24 shims contains 12 silver 60°, 12 black 90°, detailed instructions and dial chart.