In her book "Maggie's Memories" Margaret Wadkin (late of Hickling, near Melton Mowbray) describes the use of a mop nail for constructing home made mops from old pieces of cloth during her village childhood in the early 20th century. "The mop nail was made by the blacksmith (if there are any still around, they will be antiques).
This nail was several inches long with a point at the end and a flat head a couple or so inches wide., we would stand the nail on its flat head, cut pieces of old material into squares and push over the sharp end of the nail and when enough fix a piece of leather, then push the sharp point into the mop stale or handle. There was a knack of twisting these mops over the wrist to swish away surplus water, every woman could use one of these useful mops."