Engine Compression Testers

Worked as it should. Tip: lube O ring before using, or it will stick onto the head. I used it without lubing the O ring & it stuck onto the head. I had to spray pennatrating oil into the spark plug hole & let it sit overnight beforew I was able to remove the tester. I will give 5 stars. The tester is a quality product & its my fault for not lubing the O ring. I have used a compression tester many times & know to lube the O ring.