I'm fan of Mario Rubio, an excellent Spanish night photographer. I think his work is awesome. I've learned a lot of things about night photography because of his conferences and his blog.
In his website, he has a post about how to change the colour of your torch. He proposes to make colour filters with bottle caps.
Here, we are a little more "geek", and we want to review the solution of the "bottle cap". What about a changeable support with the accurate size?
I've taken my torch and I've made a support with a 3D Printer. You can view below the design of the piece.
After printing, we have a plastic piece with the correct size to plug in our torch.