This is a blanking plug for a 1/2" BSP pipe fitting. Its main purpose for me was to test the water tightness of print settings, as it is the same thread as a shower head... Where ever I am, its easy to remove the shower head and replace it with this blanking plug, then turn on the shower to check if the print can hold mains water pressure. The same print settings can then be used for other items with some confidence they will be water tight and strong enough to hold water pressure. Note there is no sealing mechanism for the threads, so it with either need PTFE tape, liquid thread sealant (adhesive) or a rubber gasket. it is common for there to already be a rubber gasket in the shower head that can be reused.