Top looks like they've used bearing locknuts. If you look around 1:29, you can see the two nuts on top of each other. I'd also guess they've used a similar setup on the bottom, as going by the general construction of that machine, I doubt they'd have a big enough tap or access to something capable of thread milling, unless they've welded the bottom ends.
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I'd also say the top plate has a slight bend in it, but it could just be the camera angle. Might be worth adding a couple ribs for some additional strength.
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Eddy, I'd hardly call that totally unsafe. Might get health and safety squirming, but given how slow it moves and the fact you're controlling it with a basic spring centred spool valve, if you manage to crush yourself with it, you deserve a darwin nomination.