Voron feet come with a M5 thread, while the KP3S feet are chunks of rubber glued to the bottom.
This is an adapter that also raises the printer a bit to allow storing tools or passing cables under.
Bolt holes are slots to allow for slight differences in models and adjustments.
Feet used - https://www.aliexpress.com/item/1005003016864277.html?spm=a2g0o.order_list.0.0.3d1e1802H0bCYY
The author hasn't provided the model origin yet.