When the fish is not feeding on the surface but is standing near the bottom, these tungsten elements are essential to be able to make some catch. Their weight allows your artificial flies to work under the surface of the water at various depths.
There are tungsten ballasts of various colors, sizes and shapes. Each of them has different characteristics and will allow you to be very effective in different situations. For example, tungsten beads with slots (to be combined with jig hooks) and jig off tungsten beads (to be combined with any type of hook) allow you to work the artificial fly with the tip of the hook facing upwards, a very useful feature when you need to make the nymph work near the bottom and you want to minimize grounding.
Tungsten bodies, such as javi, have the characteristic of being very heavy but at the same time very small. This allows you to easily reach the bottom with artificial flies of very small size, being able to deceive the fish more easily.
Tungsten dumbbell and tungsten coneheads are mainly used for streamer relatization.
The wide range of colors available allows your artificial flies to be always clearly visible in any situation. With veiled, greenish waters, an orange, purple or red beads will be much more visible than a green or blue ball. To always have maximum visibility it is a good idea to choose the colour opposite to the shade of the water in which you are fishing. While in places with a high fishing pressure it is good to offer the fish more neutral colors such as copper or black. These are only general indications, fishing is not mathematical and perhaps we love it for this reason.