The tefillin shel yad contains a knot shaped like the Hebrew letter yod that extends from the ma’abarta — the area of the base of the

tefillin through which the straps pass. In this section we present some of the laws relevant to this knot.

1) One should wear the tefillin shel yad in such a manner that the “yod” knot is positioned towards the body, while the box of the tefillin shel yad faces outward. The ma’abarta

(section of the base of the shel yad through which the strap pass) should be positioned on the upper part of the arm, towards the shoulder, with the rest of the box facing downward, toward the hand.[109]

2) If a left-handed person only has access to the tefillin of a right-handed person (or vice versa), then he must wear the shel yad upside-down, meaning, with the ma’abarta positioned on the bottom, towards the hand, in order that

the “yod” knot will be situated near the body, rather than outward. (This also applies to a person whose halachic status as right-handed or left-handed is uncertain, and must therefore wear his tefillin shel yad on both arms.)[110]

3) One should ensure that the “yod” knot does not move away from the tefillin shel yad, even while they are in their case.[111]

If one sees that the “yod” knot consistently slips away from the box of the tefillin, he may have a sofer wrap a gid (sinew string) around the knot and the box to hold it in place.[112]