Chaim Finkel asks:
Question:the halacha is that one should be mkpid to wear a hat and jacket by birkas hamazon to be mkayam the din of ituf. lecheora this din should apply only when benching on a koos as tha gmara saya koos needs ten things
The Kollel replies:
The Mishna Berurah 183:10 writes that the custom is to wear a hat and jacket even when Benching without a Kos. The Machatzis ha'Shekel on Magen Avraham 5 quotes the Shelah that the reason for this is to heighten our sense of awe before Hash-m.
Be well,
Ilan