No idea what the inches size is, sorry, but they come up a lot smaller than comparable Wintec and Thorowgood gullet widths, as all the GFS gullets do.

For example, the last Monarch I looked at was bought by a customer I'd templated a horse for. At that point I'd suggested she look for a wide fit saddle (based on a Wintec width of MW-W). When she rang and asked what size gullet width to buy for the Monarch I wasn't sure whether to suggest a W or XW. I was glad I picked the latter when I went to fit the saddle because it was only just wide enough.

 

Thankyou ☺