What is a yarn spool?
Spool knitting, corking, French knitting or tomboy knitting is a form of knitting that uses a spool with a number of nails around the rim to produce a narrow tube of fabric. The spool knitting devices are called knitting spools, knitting nancys, or French knitters.
Why is it called French knitting?
The yarn trailing down through the hole is given a tug to draw the knitted braid down through it. The cords so produced where used as piping to edge dresses. This is also refered to as French Knitting. (In Germany they’re called Nahliesle.)