Levelling a base frame for a unit - what type of adjustable leg is this

I usually build a base frame out of 4x2s for placing say a cabinet or a wardrobe on top of it. I use shims or such to get the top perfectly level with a laser.

I saw a video (below is just the image) where a chap is using an adjustable leg of some sort. Does anyone know what type of leg this is exactly, that allows you to level in this manner? And how it is fixed to the corner?

thx

All sorts available if you google it eg https://www.ebay.co.uk/itm/326161785097

Those must be it. Damn expensive