M4 x 20mm Captive Socket Button Head Screws - A2 Stainless Steel Socket Button Head Screws, also known as Dome Head Screws, feature an internal socket drive, and are fastened with a Hexagonal\/Allen key. Their Low Domed Head offers an attractive finish, as well as a wider bearing surface. Captive Screws feature an unthreaded reduced diameter shank which allows for disassembly of parts within a target assembly, without the screw falling out or having to be fully removed. This aids in both loss prevention, as well as being a huge safety feature in applications where fall out can lead to damage, machine breakdown or contamination. Captive screws are often used in applications where regular maintenance and access is required, most commonly with panels. Captive screws can be permanently locked in place or can have the ability to be fully disassembled from each component depending on application. This can be done through either partially threaded entry holes, cold welding, the use of a Captive Washer , or a retaining ring. These socket button head captive screws are made from A2 Stainless Steel which provides corrosion and oxidation resistance. All Captive Screws are manufactured to order. We aim to dispatch all captive orders within 7 working days from date of order however, this timeframe may vary and will be stated at the top of the page. For custom manufactured lengths or dimensions please contact us at and one of our team will provide you with a quotation. Please note that minimum order quantity on custom dimensions is 50 units. M4 x 20mm Captive Socket Button Head Screws - A2 Stainless Steel