What is this for?

They work good in tight places. Only good for removing since you never want to go more then fingertight on a filter .


3/4 to 1 full turn after gasket contacts base, even if that means using a filter wrench. Not a filter destroyer wrench, obviously. Some filters even have an illustration on the side, and handy numbered reference points every 90°.
Around 1990, I had an old timer for an oil customer, who has since passed away. He always insisted "hand tight." Our filters were made by Purolator, because Pennzoil owned them at the time. He installed one of our filters on a 302 Ford, which leaked, and the engine blew. He put in a claim, and our tech people tested the filter to 100 PSI. The claim was denied, because the filter didn't leak. The failure was blamed on incorrect installation. I lost the account, but got it back a year or so later, but oil only.
Moral of the story: If you don't crank that sucker down a full turn, don't blame the filter when it leaks at the gasket.

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I worked for a mechanic for awhile that had the same thing happen. He use to just hand tighten filters until he had one back off and blow a Diesel engine. He ended up buying and installing a new engine on his dime. After that he always put em on finger tight plus 1/4 turn.