Preform and knitted tubular item having a retaining edge of a single thickness and method of producing such an item

A method of producing a knitted tubular item according to which the item is knitted on a circular knitting machine provided with an n number of needles and a c number of feeders, the knit being at the start knitted on a p number of first courses on only some of the n needles before being knitted on all the needles on a q number of subsequent courses, after which the basic knit is knitted normally, wherein it is knitted on said p first courses and on said subsequent q courses an elastane yarn covered with a water-soluble yarn, and then undergoes, once the item knitted, an aqueous treatment in such a manner as to make the covering water-soluble yarn disappear, whereby it is kept on the edge of the item p+q courses of knitted elastane which precede the normal basic knit.