Here is my m84 stun grenade replica. I split up the files so they are easier to print. In my printed copy I used cotter pins and metal rings instead of printing the pins. I also choose to drill the holes for the pins and spring rather then add them to the model. The spring was something I had so I drilled a hole in the head to fit it. The secondary safety pin has no function but the primary pin retains the spool which is under spring tension. For the inner core I used a piece of scrap pvc pipe that I cut to length. Enjoy