Commentary for Kelim 23:1

הכדור – PLOTA in the foreign language.

If a ball, a mould, an amulet or tefillin were torn, one that touches them becomes unclean, But one that touches what is inside them remains clean. The objects listed here contain something inside them. The ball contains some sort of soft filling (they didn't fill balls with air back then). The mould is made of leather and is also filled with similar material. Artisans would craft their wares around the mould. The amulet and tefillin contain parchment with writing on it. If any of these items are torn, they are still unclean because they can still contain things inside them. A vessel which has a receptacle is impure even if it is not sealed shut. However, the contents are not considered to be connected to the vessel. Therefore, if one touches the contents and they are pure, he is still pure even if the vessel is unclean.

והאימום (model, shoe-maker’s last) – frame of a shoe. And all of these their outer sections are leather and they filled from the inside with hair or hackled wool/a spongy substance.

If a saddle was torn, one that touches its contents unclean, because the stitching joins them. When it comes to a saddle, the stitching attaches the contents to the saddle. The contents are part of the saddle and not just inside the saddle. Therefore, even if the saddle is torn, a person who touches the saddle (when it is unclean) will be defiled, regardless of whether he touches the saddle or its contents.

והקמיע והתפילין (the [parchment] amulet and the phylactery) – there is within the housing of leather [Biblical] portions written on parchment.

ובמה שבתוכן טהור – if one of these was defiled through [contact with] a corpse and afterwards was torn, and a person came in contact with what is within them, he is ritually pure, because there isn’t any attachment with what is within them, and there isn’t anything that is within them that is ritually impure like them.

הכאוף – like אוכף/saddle.

הנוגע במה שבתוכו טמא – if the saddle was defiled through [contact with] a corpse, just as what touches it is ritually impure, so the person who coms in contact with what is within it is also ritually impure.

מפני שהתפר מחברו (because the stitching connects it – the covering to the stuffing) – and makes it one, that which is within with the outer part.