A filter cartridge comprises a length-adjustable end cap attached to an end of a filter body. The end cap includes an annular seal, a spacer coaxially positioned in spaced relationship with the seal, and a connection member including a cylindrical neck in moveable sealing contact within the seal and in a snug sliding fit within the spacer and an imperforate flange including a seal on a radial outer region thereof. A method of joining an end cap to an end of a generally cylindrical filtration medium comprises positioning an annular spacer ring in a recess of a connection flange of an end cap; melting an exposed portion of the connection flange; contacting the melted exposed portion of the flange and an end of a filter body; and allowing the melted exposed portion to cool and bond the filter body to the end cap.