M3*40 Grade 8.8 Carbon Steel Black Button Screws

At M3*40 (3mm diameter, 40mm length), these screws handle fine-pitch assembly in small housings, cover panels, sensor brackets, and medical device enclosures. 
Grade 8.8 carbon steel provides a minimum 800 MPa tensile strength — more than adequate for light-to-medium duty precision assembly. 
The black oxide finish provides a non-reflective dark surface that blends with anodized aluminum, black-painted panels, and dark plastic enclosures.
The internal hex drive enables high torque application in tight spaces where a hex head would obstruct adjacent components. 
Compatible with ISO 7380, GB/T 70.2, and ASME B18.3 standard drive systems.
Available in grades 4.8, 8.8, 10.9; materials include alloy steel and stainless steel 304/316. OEM/ODM customization supported.