I wanted a very simple and strong organizer for my 18560 batteries. So I designed my own custom tray which holds 20 18650 batteries. ID of each slot is 19.0mm, and I find it's loose enough to easily insert but tight enough to not be all shaky. There is a slight countersink on each slot to improve ease of use.

Dimensions: 136x131x30 (mm), slots are 19mm

If you really like this design but it's too big or too small for your use case, feel free to message me and I can make custom sizes to fit your needs.