Magnetic Ball Chain Holder 4.5mm

Needed a new ball chain holder and wanted one with magnetic retention. 

It is designed to use two 16mm x 4mm magnets up to 6mm thick. I trimmed these ones down to size: 
https://www.amazon.com/Keukenket-Neodymium-Magnets-25x4x3mm-Rectangle/dp/B0BFGQBXLN/

I'm using ball chain for a projector screen mechanism that's essentially a giant roller blind and my old chain holder broke (it was kind of spindly). My old holder was improved immensely by wedging a magnet into it so the chain couldn't drift out on it's own sending the screen into uncontrolled free fall.