Tilta's 4"/10cm Threaded 15mm Rod is a 4/10cm" rod with female threading on both ends. This allows you to use optional threaded rod adapters to extend the length. As a standard practice, Tilta chamfers one end of their rods and leaves the other end with a straight cut. The chamfering makes it easier to slide accessories onto the rod, while the end with the straight cut makes for a smoother rod join.
The rod is made from machined aluminum for a balance between weight and strength, and then anodized black for wear and corrosion resistance. Please note that there is no industry-wide standard for support rod threading, so when sourcing optional rod extenders, it is best to stay within one brand.