Photo frame for vertical hanging

This is a photo frame designed so that a number can be connected together and hung vertically. One of the gallery photos shows our 9 grandchildren in one vertical display.
The part of this project that took longest was working out a convenient was to connect the photo frames together.
But first a little about the photo frame. I didn't want anything to do with glass. What does the glass do? Keep the photo clean - not worried about that, and always print another - and keep the photo flat. This I covered by making room for the photo to be stuck to a piece of card with thin double sided foam tape.
The recess for the photo is sized for a square photo cut from 6" x 4" (102 x 152 mm) photo paper.
I've designed three variants of hanging and connecting brackets. One is fixed using 3 mm x 10 long screws, The screw connectors are good for easily removing one photo frame with little risk of damage.
The second type is based on split collets. These tend to break on assembly. BTW I used D