How can all four legs of the animal be exempt from tuma if three of them are needed to support his weight?
The Gemara (by the weaver’s reed) mentions a shiur of Kedei Mapa; why is the shiur not based on the melacha of meisech itself – which (presumably) is melo hasit kaful?
Tosafos explains that each leg on its own is an Eino Yachol and the rest are the Yecholim. Rashi calls it a case of Zeh Yachol Vizeh Yachol. Seemingly, Rashi views each leg as part of the three, and is part of the Yecholim group. Nevertheless, there are other Yecholim — the other three.
This is not a case of Safek, where we can’t Pasken on all sides together to depend on the rest. This is a question of who carries the weight, and the answer is that none of them can be said to be carrying the weight.
Rashi explains this Kanne to be the pole that goes up and down. This sounds like part of the mechanism that controls the headle, perhaps the treadle or a variation thereof. There is no such thing as a loom meant for a Melo Sit Kaful. The gemara is saying that the pole is big enough to control two cloths — either on diferent looms or on a wide enough loom.