I think I actually found them. Seems to be about the right dimensions to the ones I have on my planck.

https://www.amazon.com/gp/product/B01HJ64I00/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

1/4 inch in diameter, and 1.5mm in height.

I've been looking for lower height ones and I think these are what jack was using with the cases.