One of the melochas of Shabbos is “kosher” or tying. The gemorah in Shabbos 113a says that it is forbidden to tie a knot on Shabbos. There are differences of opinion regarding which kind of knot the gemorah is referring. Rashi says that any knot meant to hold for a long time is forbidden, while the Rambam says that the knot must be a professional knot. (e.g. a fisherman’s knot). The Rama 317:1 is stringent for both opinions. Furthermore, being that we are not aware of exactly what is considered a professional knot, the Rama is stringent that any tight knot is considered professional. (a double knot). However, any knot that is made to be temporary and is also not the kind of knot that is tied tightly, may be tied on Shabbos. (See Shaare Teshuva 317:1). Therefore, there are many poskim that permit tying a scarf or a belt with a double knot.

Rabbi Tzvi Aryeh Hyman, Mir Yeshiva
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