Brands offering interchangeable headplates are talking about the angle of the headplate. WOW has headplates in the U range starting at 73 degrees – very narrow - through to 143 degrees – 8X wide. All WOW saddles can take any of these head plates (as well as the V and UU headplates) because the tree is flexible enough at the front to stretch from 73 degrees to 143 degrees. Other brands cannot do this angle change in a single tree.
In addition to changing the angle WOW offer three ranges of head plates – the V head plate, the U head plate and the UU headplate. The V headplate has a very closed head, the U is the middle or normal arch and the UU has a very wide arch or hoop allowing for horses with very wide spinal processes and surrounding musculature.
A 1 V, 1U and 1UU headplate are all the same angle and fit, it is just the arch at the top of the headplate that changes in width. This means as your horse puts on muscle but does not change the angle of the withers, WOW can change.