Tifosi Carbon seat post

oldwasp Posts: 27
edited December 2012 in Road buying advice
Merry Christmas

One of my prezzies is the Tifosi Carbon seat post and it has a collar on it, this slides up and down the post and can be tightened with an allen key. It is shown in the pictures on some of the websites it is sold, but what is it for?
I am new to all of this and have not tried to fit it to my bike yet but was hoping to try it out boxing day.