(Wow! It appears this is used as a prop in Netflix series "3 Body Problem") See the latest Make that I posted with photos clipped from Season 1 Episode 1. This is my first time as a prop designer :). Btw, I loved the 3 Body Problem series, I hope we have a season 2 soon.

<Updated with a little tongue and groove to help place the two halves and provide better capillary action when glueing. Much thanks to user Ridley for the design tip! >

This is a "two parts in one print" design with no raft or supports needed.
Print the "DNA_Helix_Pencil_Holder_Full_06.stl" STL file

1. After print, remove two parts from print bed.
   a. bottom of helix is outer print
   b. top of helix is inner print.
2. (Optional) Use "DNA_Helix_Pencil_Holder_Optional_U_Snaps.stl" x 2 on the outside of the helix to secure the top and bottom parts together. These are pressure-fit snaps that fit on the outside of the Helix. Use a screwdriver to gently lever them out if you need to remove them.
3. Assemble with glue, or your favorite adhesive to make the bond permanent. (I used super glue). With the snaps in place glue may be optional.
4. Insert Pencils and display.
5. Take a picture and post on Thingiverse :)

I also have a Sharpie version: http://www.thingiverse.com/thing:1924310
I've also had requests for a smoother version: https://www.thingiverse.com/thing:2789838