M4 x 40mm Socket Flanged Button Head Screws (ISO 7380-2) - A4 Stainless Steel Socket Flange Button Head Screws feature an internal socket drive and are fastened with a Hexagonal\/Allen key. The Flange Base on the head of this screw also acts in place of a washer, distributing the force of the fastening over a larger surface area, making it more secure, and putting less stress on the fastened area. These Socket Flanged Button Head Screws are made from A4 Marine Grade Stainless Steel which provides corrosion and oxidation resistance as well as increased resistance in harsh chemical and outdoor environments. For larger quantities or custom sizes, please email and one of our team will provide you with a quotation. M4 x 40mm Socket Flanged Button Head Screws (ISO 7380-2) - A4 Stainless Steel