Shabbat 78 - Useful small amounts
It is forbidden to carry in a public area on Shabbat. How much? - Enough to be useful. For example, oil - enough to anoint a small limb of a small child; rope - enough to make a handle for a basket; paper - enough to write a tax collector's receipt; erased paper - enough to make a bottle stopper for balsam oil.
Hide - enough to make an amulet; parchment (thinner, processed hide) - enough to write the smallest paragraph of the four paragraphs that are written inside a tefillin; ink - enough to write two letters. Why two and not one? - Because in the Temple the beams were marked with letters, so that two specific beams would always be assembled together. Eye paint - enough to paint one eye - because in some countries women would go out covering their head and leaving an opening for only one eye.
Art: Dirck Hals - Woman Tearing a Letter