Ya gotta love s2ki.com.

From reading this thread, it's either a 1/4", 3/8", 1/2" or 3/4" square drive in the center of the piston.

For me, a 3/8" extension worked almost as well as the little cube-shaped tool with an extension.

 

Damn I wish I had a pic of the tool I made.

Basicly welded 4 pieces of metal to a small square of metal then welded an extension to it.

You could buy one of the squares but I think it is more fun to make tools. And mine works sooo easy.