4ply is a light weight yarn suitable for knitting and crocheting lightweight garments, tops, shawls, baby and children’s clothing, socks and accessories. 4ply is the equivalent referred to in the USA as fingering,..4ply, fingering, and sock weight are very similar in thickness.. 4ply wool is light but cosy and knits up or crochets on 2.5mm to 3.5mm needles or hook as a guide..