No matter what type of dumbbell eyes you’re using, it’s important to understand that regardless of tie-in method, with enough pressure, they’ll rotate around the hook shank. In other words, don’t expect a permanent weld.
Begin by getting your thread started on the hook shank in the appropriate location. Place the eyes diagonally on top of the shank and take a couple of cross wraps both ways to lightly secure them. Follow this with over the dumbbell, under the shank wraps as shown here. Use enough pressure so it’s like a mini tug-of-war back and forth. Then take a single wrap around just the hook shank and begin making circular wraps beneath the eyes but on top of the shank. This will pull the previous wraps together as well as create a little shelf on either side of the shank, to further stabilize the dumbbell.
Finish by taking several wraps around just the hook shank to effectively save your work. Once again, this isn’t a permanent weld but the eyes are lashed to the hook shank pretty darn tight.
I’ll also use materials in the fly to further prevent the eyes from rotating.