Not much, based on the one which I have. It is a triple lead Acme thread, and comes in fixed length sections, with D shaped projections to couple between sections. The "nut" part of the follower is long enough so it bridges the gaps.
When I discovered that the set would not fit where I needed it to (an enclosed I-beam sort of limited the positioning of the motor assembly), I called the makers, and they said that it was "impossible" to get non-standard length sections. Well -- a bit of lathe and mill work and I had a shortened section of leadscrew and guide rail extrusion so it would mount and work -- so much for "impossible". :-)
But there is no practical way that it could handle much load from above -- too much pull on those couplings, which are just push-in and a spring to clip them there. There needs to be a bearing at the far end of the guide and leadscrew to handle the load.
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Rollers on each side, and rollers offset to the bottom on the load side and to the top on the opposite side. The rollers could be in-line skate bearings for cheap and easy to find.
But I don't see a leadscrew as practical -- especially multi-section ones as implemented in garage door openers.
And there are big springs taking up the weight of the garage door so when the nut is uncoupled (at the pull of a red string) it does not take much human force to start the door on its way up. Maybe about ten pounds ta a guess.
Enjoy, DoN.