These screws are T6.

A long flat-tip screwdriver can be used to push the tab out from the other side as they hook inwards towards the center. You can see the locations in the step 4 photo near the edges.

I replaced the little disc that Jesuis Une was talking about with a piece of PTFE used for mouse skates. The disc is 5/32 or 4.0 mm. I used a punch to knock a piece of 0.6 mm PTFE from the excess edging and it works like a charm.