Features: A strong spring for three-D Printer Extruder. Excellent elasticity, fatigue resistance. Nickel plated, corrosion resistance, high hardness. Specifications: Material: 45 carbon steel Item color: silver tone Wire diameter: 1.2mm/0.05" Outer diameter: 7mm/0.28" Inner diameter: 5mm/0.20" Spring height: 20mm/0.8" Ring quantity: 9 rings Surface treatment: Nickel plated Package Included: 30 Pcs 3D Printer Extruder Strong Spring