In my experience, many templates in the US, such as UA's, are hinged, so if your bag doesn't fit (mine is 'a bit' oversized), just lift the template and let it sail through. Thus far, the screeners have not objected, nor has my bag been gate checked. However, as pointed out above, overseas operations can be quite strict. For example, if you are boarding TG in many cities outside of BKK, good luck with your rollaboard, even if it is a standard size (unless you are a top-level ROP member).