3 Star Inc's 7510-M / 7510-F N or PL-259 metal screw on dust cap. These silver plated dust caps are great for transporting your cables and for people and applications on the go. They help prevent dust and moisture from getting into your coaxial cable connectors which can cause havoc on your RF setup.
They will fit into the end of a N or PL-259 connector. Caps are available with male or female threads, just select the gender you want using the dropdown options list.