The heads of the nymphs play different roles during fishing, they attract fish by their flashes and color, thanks to their weight they enable the nymphs to sink quickly to fishing zone and keep flies in the right position which is most effective.

Slotted beads are necessary when you want to use a larger bead on a smaller hook - very popular in modern Euro-nymphing. The slot allows the bead to roll around the bend of the hook when threading the point through the small opening on the front of the bead. We prefer the Hanak beads because the small round opening on the non-slotted side of the bead is typically small enough to prevent the bead from coming off the front of the hook (the eye of the hook is, in most cases, larger than the small round hole in the bead).

Tungsten has a specific weight of 18 kg/dm³, which is nearly twice more than the lead.
Therefore your flies can be slimmer and tinier, and more attractive for fish. Tungsten nymphs are absolutely essential for fishing in deep pools and fast streams.