Qh Bars?

I have a simple enough question.

In western saddles, what are the bars? Do you know what I mean?

Like people say
FQHB or QHB or stuff like that. How do you know what your saddle is?

Size of the tree.

AQHAs being wider, a AQHA bar would mean a bigger (wider) tree span.

I'd just suggest to google. There are plenty of resources with pics on internet showing different parts of the western saddle (with explanations). Like this one: Western Saddle Fitting and Different Tree Sizes