My prints all fit into one of 5 sizes of IKEA frame.
I used to sell the smaller sizes mounted so that a buyer can simply slot the mounted print into the frame. However, the mounts were very vulnerable to damage in transit. The 26x17 prints fit into the mount supplied by the IKEA frame and many other typical A4 frames.
The 39x13 prints will require a mount to be made to fit into the IKEA frame (50x23cm frame) which comes with a mount for 3 photos. The mount size is -external measurement 50x23cm the margin is 4cm and the opening is 42x15cms
The 13x13 cm prints fit in the 23x23 cm box frame and require a larger opening than the frame comes with. The mount needs to be 23cm x 23cm with a 3.5 cm margin and the opening is 16x16cm.
The 2 larger sizes (25x25 cm print and 34x24cm print) fit the mounts supplied with the frames. ( see frames below).
This means that you can send a print as a gift to anybody around the world who lives near an IKEA (and they are everywhere) and they will easily be able to afford to frame it.