The document analyzes the basic structures of weft knitting fabrics. It describes four primary structures: single jersey/plain knit, rib, interlock, and purl. Each structure is defined by its appearance, extensibility, edge curling properties, ability to unravel, and common end uses. The single jersey/plain knit structure forms the simplest balanced fabric. Rib structures require two needle beds and form fabrics with faces of loops on both sides. Interlock fabrics are locked on both sides but can be stretched. Purl structures involve special needles and form fabrics with horizontal rib effects.