What is an oem?

An OEM part is the one the manufacturer specifies. Aftermarket parts are made by third parties and vary enormously: some are identical or better, some fail within months. For safety-critical or hard-to-reach components — anything requiring a teardown to fit, or anything in a gas or high-voltage circuit — OEM is usually the honest recommendation, because the labour cost of doing the job twice dwarfs the parts saving.