Nickel Plated Carbon Steel: T hammer head bolt, high quality nickel plated carbon steel, good rust resistance and better performance. Detailed Sizes: Hammer Head Size: 17.7 x 7.7 x 5.5mm; Thread Diameter: 8mm(M8), Bolt Length: 25mm. For 40 Series: High quality T-slot bolt screw for 40 series metric aluminum profiles, fit for most 40mm aluminum profiles. < p>Widely Used: Widely used for building 3D printers, 3D carvers, CNC routers, CNC laser cutters, CNC plasma cutters, robotics projects, machine guards, workstations, etc. Pack of 10: 10 M8 x 25mm bolts.