Chapter 42: Turning the Yad Tefillin into Rosh Tefillin
- Turning Rosh into Yad: It is forbidden to convert a head-tefillin into an arm-tefillin.
- Using straps of Rosh for Yad: This applies even to the strap. Thus, it is forbidden to take a strap from the head-tefillin and use it for arm-tefillin.
- Turning Yad into Rosh: It is permitted to convert an arm-tefillin into a head-tefillin.
- New Tefillin: If the tefillin have never been worn, it is permitted to convert even a head-tefillin into an arm-tefillin.
- How to turn a Rosh Bayis to Yad: This is accomplished by overlaying it with a single piece of leather, so that it appears like one compartment.
Halacha 2: Stipulation
- If on the outset one stipulated that he desires to convert the head-tefillin into an arm-tefillin, he may do so, even if someone later wore it on his head.
Halacha 3: The Tefillin bag
- If a bag was designated to permanently house one’s tefillin, and was then used once to house the tefillin, it may not be used for a mundane purpose, such as to hold money.
- Stipulation: If at the outset, one stipulated that he would be able to use the bag to hold money, then he may do so.
- Sanctity of Kelaf: If one made a parchment for tefillin, he may not use it for mundane purposes, such as to write on it.
- If one never used the bag: If one never used the bag to hold tefillin, then one may use it for money even if it was already designated for Tefillin use.
- Used for Tefillin but never designated: If one used the bag to hold tefillin but never designated the bag for this purpose then it may be used for money.
 See “The Laws of Tefillin” Chapter 6 Halacha 19