All of them are made of high hardness nickel plated carbon steel, with good rust resistance and better performance, durable for long time usePackage: This kit include 40 series M4x40pcs, M5x30pcs, M6x30pcs 100pcs stored in a transparent plastic box, convenient for your storage and useFeature: They can be directly into the aluminum slot hole in any of the assembly post, back spring ball can be fixed its position which make installation very simple and reliableApplication: T-Nuts suitable for 4040 series aluminum profile, widely used for building industrial aluminum frame structures, 3D printers, CNC Routers, CNC cutters, robotics projectsProduct Type: Hammer head drop in T slot nuts assortment kitModel: For 4040 series aluminum profileHead type: Hammer HeadMaterial: Nickel-plated carbon steelThread Size:M3 M5color:silverPackage Contents:40 x Profile Nuts30 x M5 Profile Nuts30 x M6 Profile NutsOnly the above package content, other products are not included.Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.