Fly Tying Bead Head Size Guide
Match tungsten or brass bead head size to your hook size.
Get recommended bead diameter, bead weight, and approximate sink rate improvement.
Why Bead Head Sizing Matters
The bead head must fit snugly against the hook eye without being so large it slides over the bend or so small the hook eye disappears inside the bead. The bead hole must be smaller than the hook wire at the bend (to hold the bead in place) but large enough to thread the hook point through during assembly.
Most commercial tungsten bead sizing charts match bead outer diameter to hook gap width. As a rough guide, bead outer diameter should be roughly equal to or slightly larger than the hook gap width (the distance between hook shank and point tip).
Tungsten vs Brass
Tungsten density: approximately 18.0 g/cm3. Brass density: approximately 8.5 g/cm3. For the same bead size, tungsten weighs about 2.1 times more than brass. In water, the buoyant weight ratio (accounting for water displacement) is about 2.3 to 1. This means a tungsten bead sinks roughly twice as fast as a brass bead of the same diameter, and allows the fly to reach the strike zone faster in faster water.
This calculator shows the approximate weight per bead for both materials, letting you judge whether the added weight is appropriate for the water conditions you are fishing.
Standard Sizing Chart
Hook 22-18: 2.0-2.4 mm bead. Hook 16-14: 2.8 mm. Hook 12-10: 3.2-3.5 mm. Hook 8-6: 4.0-4.5 mm. Hook 4-2: 5.0-5.5 mm. These are starting points; exact fit depends on hook wire gauge and bead brand tolerances.
Slotted vs Round Beads
Slotted tungsten beads have a notch cut into the hole, allowing the bead to sit closer to the hook eye on jig-style hooks (Hanak, Dohiku style). Round beads are standard for straight-eye hooks. Slotted beads on jig hooks produce a keel effect that reduces snags significantly.