Unless I'm doing something very, very, wrong -
It seems the numpties who designed the Screwfix site and the morons who signed it off decided it would be a good idea to list screws - not in size order - but instead give the customer the choice of sorting by
Top Sellers, Price High to Low, Price Low to High" Product Brand A-toZ, product Brand Z to A, Average Star Rating. None of which bring up a size sorted list but a mixture of individual sizes.
Which is total bollocks. You chose your sort categories according to the characteristics of what you're selling. Without checking maybe this is a straight port of the B&Q abortion. The only surprise is that they didn't include "sort by colour" as well.