> If you say "one bar of butter", "one stick of butter", and "one pat of butter", these can all refer to three different things or the same thing, depending on where you are located. East Coast and West Coast US butter are sold in different size blocks (though both are "8 tbsp") however sometimes you'll find 4tbsp sticks on the west coast that look like 1/2 an East Coast stick that I've heard called pats.

Wat. Never in my life have I seen butter in the (mostly western) US sold in anything other than 1/4 lb sticks. There are long, skinny sticks and short, fat sticks, but they're always 1/4 lb. If you say a "pat" of butter, you're getting roughly a 1/2 Tbsp of butter from me. Definitely not half a stick!

Midwest, East Coast, and South I've seen some 1/2lb or 1lb blocks for fancier butters sometimes. But a pat of butter was definitely 1/4-1/2 tbsp of butter in the midwest - depending on if for toast (less) or for baking (exactly 1/2).

I've not heard "pat" used as a serious unit of volume since childhood though. In fact I rarely hear the word pat in relation to butter at all anymore.