On Fri, 27 Feb 2009 01:17:26 +0000 (UTC), David Lesher
wrote:

"David Merrill" writes:

For pulling use a hollow ram with a pull rod through the center, powered by
a hydraulic hand pump.

Hmm. So the shaft passes all the way through the piston; while the
piston pushes the cup.

Many of the jacks have threaded extenders; if you pull same, what is
under it? Is the whole piston hollow?

The piston is hollow but you will pull the thread insert out.