See the hook and bead chart in the product photos for information on matching hook size and bead mass.
These are top quality tungsten beads at a great price with small slots to increase weight.
Slotted beads are great for jig hooks but I also use them for straight shanked hooks as well. By inserting lead wire into the slot you can offset the bead to increase hook gap and the hold of the hook while also inverting the fly in the water. The colored beads allow you to add an extra flare or a hotspot to your flies. The 3.8mm beads fit into the FIPS Mouche measuring device so you'll know you're legal if you fish in FIPS governed competitions.