Metric Nitrile O-Rings are one of the simplest, yet most engineered, precise and useful seal designs ever developed. This assortment of O-rings features a variety of metrically-sized parts measuring 3mm and 4mm wide. O-rings in this assortment are made of high-strength Nitrile (Buna-N) rubber. O-rings are ideal for myriad applications. DIY projects, plumbing services, and contracting work are made easier with Hillman O-rings. Full assortments of #56272 contain eight (8) refills comprised of Hillman item numbers #56273 - #56280.