What's the difference between a fitzwilliam & a trifold girth?

I was looking on a few websites that state they sell fitzwilliam and trifold girths for sidesaddle use but I’m not sure what the difference between the two is? I know what a trifold girth is/looks like but I’m not sure what a fitzwilliam is/looks like. Is one preferred over another? If so, why?

Tri fold or Fitzwilliam?

The standard Trifold leather girth about 4 inches wide after the leather is folded and the the buckles are sewn on. Two on each end.
The real Fitzwilliams girth is wider. They can be up to 6 inches wide and made of English Bag hide. There are two buckles on each end. There are leather straps sewn on as keepers for the overgirth which slips into the keepers and is about 2 inches wide with one buckle on each end. The origial Fitzwilliams were web. Then they became popular in the Foxhunting Field in the 1920’s -30’s. They made them of leather for the Hunt field.
For sidesaddle either web or the leather is correct. They hold the saddle in place securely and help keep it stable on the horse. There are some low quality Asian imports that claim to be Fitzwilliams but they are not. They are cheap imitations of the real thing.
The real Fitzwilliams girths out of England are not cheap. But if you are going to go into a class with appointments, perhaps Corinthian Hunters (ultra formal) then you might want to invest in a Fitzwilliams girth.
I hope this answers your question. I have photos but would have to Email them to you privately.
Kind regards, Sadlmakr

Fitzwilliam; http://www.sidesaddlesource.com/MVC-017S.jpg

http://www.wendyssaddlery.com.au/side_saddle_accessories.htm

Thank you very much! That makes sense. I believe I’ve seen some photos of them, I just didn’t know that those were fitzwilliam’s. Your description was very helpful!