It is generally considered illegal to use an oil filter for a solvent trap. Law enforcers are well aware that a solvent trap is often used as a rifle suppressor. In 2012, a man was slapped with a two-year prison sentence in a federal penitentiary after being caught in possession of an oil filter, an adapter and a threaded rifle.
The concept of using an automobile oil filter as a rifle suppressor started around 2012 and became a viral Internet sensation. One particular ammunition company started selling a registered NFA suppressor made up of an adapter that connects a car oil filter to a threaded rifle barrel, and other individuals followed suit by using common thread adapters to make illegal suppressors.
These suppressors were dubbed as "solvent traps" to trick law enforcement into believing that they are only meant for use as traps to catch cleaning solvents that may leak out of the barrel during cleaning. However, law enforcers do not accept this reason, as any random metal or glass container and even a piece of throwaway cloth can easily be used for the task.
Being caught with using an oil filter as a rifle suppressor can mean losing one's license to carry guns. It's best to save up and buy a professionally made rifle suppressor instead.