These cap head hex socket screws are made of steel with oxidation surface, which are resistant to rust and corrosion. There are 9 thread lengths for you to from, which can be generally used and office appliance, machinery, furniture, etc. 1. steel material with oxidation surface has good strength of extension and corrosion resistance in many environments. 2. Cap head enables driving where it doesn't have sufficient space for wrenches. 3. perfect for use in confined areas where the head needs to be flush or the surface. 4. Used for fasteners and office appliance, communication equipment, assembly or other machinery industry. 5. Screws and nuts are packed in 10 compartments and in a transparent plastic box for convenient use and storage. Material: Carbon steel Color: Black Screw Thread Lengths: 4mm(20Pcs), 5mm(20Pcs), 6mm(20Pcs), 8mm(20Pcs), 10mm(20Pcs), 12mm(20Pcs), 16mm(20Pcs), 20mm(20Pcs), 25mm(20Pcs) Thread Diameter: 3mm () Size: 12.5*6.2*2.2cm Type: Cap Head Hex Socket Screw Function: Fastener Package Includes: 180 x Screws 100 x Nuts Only the above package content, other are not included. Note: Light and different displays may cause the color of the item in the a little different from the real thing. The measurement allowed error is +/- 1-3cm.