Mini Delta Ribbon (MDR) Jack Socket Screw These 3M Jack Socket Screws are for Mini Delta Ribbon (MDR) connectors, they are stainless steel with a M2.5 main thread with the head having a #4-40 UNC socket thread. The design of these Jack Socket M2.5 Screws include a thread locking insert. What are MDR Connectors? Mini Delta Ribbon connectors, or MDR connectors, are a type of D-sub connector designed to accommodate flat ribbon wiring with pre-loaded ribbon contacts. They are typically used on PCB boards and combine excellent mechanical strength and connection conductivity. Why choose 3M? 3M is a trusted name in connector and wiring solutions, providing high quality cables, connectors and accessories. From industrial computing to domestic applications, 3M provides the reliable and versatile product range you need.