This model of a spear head is in two parts that glue together.  The socket threads onto a mop handle or paint roller extension that has ¾" (19 mm) thread.  Then glue the spear point into the slot.  The threads on mop handles are often not very precise, it might be a good idea to print the first couple threads of the socket to make sure it fits before printing the whole thing.  You can scale it up or down a little to make the threads fit better.  This is intended as a prop for dressing up for Halloween, but it is pointy.  Be careful.