Time aircraft engines with precision.The Arrigetch Design Piston Stop is custom made to work with our Digital Magneto Timer. Video Instructions Printed Instructions It is compatible with virtually all horizontally opposed aircraft engines using 18MM spark plugs, especially Lycoming and Continental.Features Synthetic material has no potential to scratch or mar piston (unlike metal piston stops) Piston Stop is reinforced with a central steel pin to eliminate any strength concerns Tool-free design threads in quickly and easily by hand Warranty and Returns: I stand behind my products. All Arrigetch Design products come with free 30 day returns and a 5 year warranty. For returns or if a product is for some reason unable to perform its specified function, send me an email to [email protected], and I will personally refund or replace it. -Taylor