Threaded Lens Cap Holders for Camera Strap

Inspired by Teds lens cap holder I created my own design, because I wanted a few improvements:

* a __proper thread__ that holds the cap as good as the lens or filter itself (0.75 pitch)
* closed bottom to protect the cap (thin bottom, therefore not really more filament)
* option for two different sizes of caps when changing the lens (__double__ version)
* proper fillets to avoid sharp edges

I've tested the holder in my recent vacation trip and it turned out to be very useful. No more searching for the cap in the pockets and due to the thread it held on the holder as good as on the camera - never dropped it.

The holder is designed for a 40mm camera strap and can be mounted easily without removing the scrap (just fold it and slide it through the gap)

Besides the "__single__" version I created a "__double__" with two rings which can either hold the cap of my normal zoom or the big tele lens. And as the cap of my big tele lens has a diameter of 86mm I also created a "__slim_