Working on your classic Datsun Z engine? This is a genuine Nissan OEM manifold stud. The part number is 200-784, and it's used to attach the exhaust manifold or intake manifold to the cylinder head on 1970 through 1978 Datsun 240Z, 260Z, and 280Z models. These studs can rust, seize, or break over time, especially the exhaust ones due to heat. Having proper OEM hardware is key for a reliable repair. It's brand new in its original Nissan packaging. If you're doing a head gasket job, manifold swap, or just fixing a leak, replacing old, questionable studs with new ones like this is always a good idea. It ensures proper clamping force and prevents future headaches. A small but critical part for your Z car restoration or maintenance.