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Photo © Wenzai
Sounds like you are reffering to aircraft hydraulic jacks.
These are hydraulically operated,screw jack ring locked at small intervals of lift to cater to a loss of fluid.
Placed at four points around the aircraft "normally".
There is a level plumb bob/spirit level in MWW normally used to monitor the jacking process to ensure equal mvmt.
[Edited 2008-12-17 12:49:53]