Nano Silk Pro 20D is considered the professional level being the finest of the range. 20d is also known as 24/0, that is really very small indeed! That said this baby of the Nano Silk family has all the strength you would expect from this premier thread. It is 10 times stronger than steel of the same diameter! Nano Silk Pro 20D is fine enough for size 20 to 32 flies whilst still retaining its strength. Available in black and white, with 100 metres on each spool, if you dare, you can split this oh so fine thread further if required so dubbing on size 32 flies with split threads is a reality!