Size 10 & 12
Pack of 3
It is best fished quite slowly as a middle dropper fly on a long leader as part of a team of nymphs, or static with buzzer pupae imitations.
This is a Welsh pattern (the name mean 'Little Devil') that proved to be very successful when it was first introduced to Chew and Blagdon. From there is has successfully transferred to other waters and it is now one of the most popular general purpose patterns around.