Adjustable decking posts

[Handygal]

:?: Has anyone heard of (and know where I can buy) adjustable metal posts that will support the decking frame? This was mentioned to me by a builder friend but he didn't know where you can get them. A threaded metal rod is fixed into a concrete footing, then a second rod threads onto this and supports a U-shaped saddle for the decking joist. This works in the same way as a traditional wooden post in concrete but the second rod means the horizontal level of the frame can be adjusted slightly.

I'm constructing a large area of decking (20ft x 16ft) on a relatively flat surface but this ajustable post would make my life a lot easier!

Thanks in advance for any advice you can give. :D