ECO/N refers to our Ecomicron element. It is an all plastic construction, designed to be Incinerable and to allow for lower shipping costs. MM refers to our Mobilemicron element, designed specifically for the mobile market. Its lightweight construction also has the added advantage of a low clean element ?P per flowrate for cold start conditions. A higher dirt holding capacity allows for fewer element change-outs, saving both time and money. W/HC and P/HC refer to wire mesh and paper media, respectively. These are both surface filtration elements (nominal), refer to #3 above. AM refers to our Aquamicron (water removal) element. This element is designed to remove free water from oil. Water retention capacities are provided in the Aquamicron sales brochure.