Under Jacking Points in The 2005 rulebook one of the criteria is that:
D) Exposed around the lower 180 degrees of its circumference over a minimum lenght of 280 mm(11 in)

Can someone explain exactly what they me by this it unclear to me.

the jacking point must be a tube that is unobstructed for 180 degrees of its circumference, meaning a full semicircle has to be available to the quick jack. And the tube must be atleast 11in long.

I hope this helps at least a little.