3 pack - the Hydronix swc-45-1020 polypropylene string wound filters have a particle retention size of 20 micron and are used in a residential and commercial water filtration system applications. The filter has an outside diameter (OD) of 4.5" and overall length of 10". made of 100 percent pure polypropylene cord, the cartridge has structural stability, and is resistance to most chemicals. The swc series filter is suitable for use in filtration systems such as residential water filtration, whole house, well water filtration, ice machines, film processing, beverage, coffee, analytical, wineries, and many others.