Commonly called 4 ply in the UK, they are also known as fingering yarn or sock wool. So what’s the difference? The term 4 Ply traditionally referred to the fact that the yarn was made up of four plies. Now it is more often used to describe the thickness of the yarn. Sock wool is often blended with another fibre, usually nylon or has a tight ply twist. This makes them stronger, more durable and yes you guessed it. A good choice for socks. Fingering weight yarns are not typically blended with any other fibres for strength, can be made up of fewer plies and may have a looser twist. I recommend using 2 to 3mm needles and hooks but always refer to your pattern.