Reddit mentions of 10'' Wooden Hand Screw Clamp

(I've been meaning to add this as a tutorial on my blog but I've never gotten around to it. Hopefully, this will give me a start and the energy to follow through with it.)

1. Acquire jumping jacks, a big wooden clamp, a pane of glass and another wooden clamp (if you fear for your lens)
   
   
2. Find the hole in the side of the jumping jack. This is where the fire will shoot from.
   
   
3. Secure the jumping jack in the wooden clamp with the hole pointing across the field of view (not toward the camera!)
   
   
4. Frame up the shot as desired. (I wanted the flames shooting into the corners.) The fire will be bright, so set your camera to handle it in a way that will give you a long shutter speed even with the bright light so you can catch the spark trails. (I used a 105mm and cranked down the f-stop to 40, but if you have an ND filter that may be the way to go.) I also hung a black cloth across some light stands behind the jumping jack and waited until dusk so I could get a solid black background.
   
   4a) Put the protective pane of glass in between the fire and the camera. It may cause some glow and reflection, but it beats burning the coating off of your glass. After about 15 successful burns I was convinced enough to remove the glass for a few shots.
   
   
5. Light the fuse and be ready with the remote. Depending on your shutter speed, you may have a narrow window to work with. I waited until the moment the fuse burned down into the body to open the shutter.
   
   
6. Check out the results. Reload and repeat until happy.