I have the 540 and I just measured it at 7" as well. My manual includes both the 540 and 550 so I will have a quick flip through it to see if this is even mentioned in it.
My machine is 20 years old, if you are considering buying a 550, it is probably about the same age.
I was going to welcome you to the board but see you have been a member for awhile....
Last edited by thimblebug6000; 05-07-2018 at 04:49 PM.