Copper tubes lined with plastic insert for tying fast sinking tube flies. Sold here in the small (3/32") diameter and the large (1/8") diameter in 1/2", 1" and 1.5" lengths. The small diameter offers a fast sink rate and the large diameter offers an extra-fast sink rate.
These are sold 10 per pack with clear junction tubing and liner tubes.
The large will accept Large Coneheads or can be nested with micro tubing and small beads and the small will take medium tube cones or medium beads.