925 sterling silver. Tubes are available in two sizes: outer diameter: 1.8 mm, inner diameter: 0.7mm, length: 1.8 mm (also available gold-plated) or outer diameter: 2.0 mm , inside diameter: 1.0 mm, length: 2.2 mm. Sold in packs of 100. When pressing the tubes it is best to use the wires intended. The smaller size fits 0.35mm wire and the bigger 0.45mm wire.