Everyone knows that the purpose of an engine's oil filter is to remove particles that can cause internal engine damage. Critical clearances within today's engines are typically measured in thousandths of an inch and, in some cases, ten-thousandths of an inch.

So what size particles should our oil filters actually remove? And how much material should an oil filter capture and hold? Ramon Nuñez, spokesman for Purolator Filters NA LLC offers some information.

Purolator (which stood for "Pure Oil Later") was first made available in 1923 and subsequently the full-flow oil filter was designed to filter 100 percent of the oil during every pass through the engine. Nuñez said, "A micron is a millionth of an inch. Our research shows that, in general, particles larger than 20 microns have the potential to cause internal engine damage."

So, when it comes to particles, how small is small? Nuñez provides some comparisons to explain just how efficient their oil filters really are. A strand of human hair is anywhere from 30 to 200 microns. A typical grain of beach sand is larger than 100 microns in diameter. And some bacteria can measure 20 microns or even larger, while a virus can measure a miniscule 0.005 to 0.1 microns.

And what about capacity? How much debris should an oil filter be able to hold? Purolator's Nuñez explains that capacity is critical. Quality oil filters normally incorporate a by-pass valve to allow unfiltered oil to reach the engine in case the filter becomes completely clogged. While unfiltered oil is better than no oil at all, it is still potentially damaging to the engine. And since there's no way for the driver to know if their filter is clogged, it's vital that the oil filter has a large enough capacity to supply properly filtered oil to the engine for as long as possible.