A hydraulic tool assembly for a downhole tool comprises a body (12), first
and second members (14, 16) mounted for independent movement with respect
to the body, and first and second control fluid chambers (24, 26)
associated with the respective first and second members. Movement of the
first member (14) between a first position and a second position in
response to an applied force displaces control fluid from the first
chamber (24) into the second chamber (26), to move the second member from
a first position towards a second position to execute a tool function.