Using a file without a handle on is a potentially dangerous concept, what with this spike being moved around rapidly in front of you and with great force, often in the squishy part of your palm. Much safer and more comfortable to use a handle on it. Also you can hang them up with the loop provided in the handle, or use the handle to stop them dropping through your tool rack.
Two sizes are provided as STL's below in the traditional manner; too big, and too small. Fortunately they scale well.
Print, bludgeon spiky end of file into star-shaped hole in the handle. If you are sure you're not going to want to swap the handle, warm up the spike or add glue to ensure a permanent fix. Generally though, whacking it in works.
Because it's tall and thin you will probably want to use a raft to ensure good base adhesion. If printing small ones, you may want to print two at a time or the skinny bit may well blob.