Cathbard

http://www.stewmac.com/shop/Tools/S...he_Gripper.html

You can make something similar yourself with an allen bolt a piece of surgical rubber tubing and a couple of nuts. The bolt has to fit in the hole, tubing that just fits snugly in the hole around the bolt. Then screw down the nut to distort the tubing, then use the second nut as a locking nut to hold it all in place and give you something to hold onto with a spanner/socket. You'll probably need a washer between the head of the bolt and the tubing depending on the bolt you use.

I've also done it using a pair of needle nose pliers pushed into the hole and pulled open to grab the jack while you tighten the nut on the jack. I had a pair that I ground the back of the jaws flat so there was a corner to bite into the inside of the jack. That worked too.
You could also modify a pair of outer circlip pliers the same way so you squeeze to hold the jack still rather than trying to pull the handles apart like you have to with pliers. Some circlip pliers already have corners on the jaws so no modification is even needed.

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Cathbard Amplification