Pashtus is that it has to be covered. The Gemara might imply that it’s okay if it’s in a place that’s usually covered (the arm) but not actually cover. Many are Machir to cover it completely, including the Retzuos. (This is a Drasha of Ukshartam L’os Al Yadecha- Lecha L’os V’lo L’acherim L’os.)
Menu