Gemara

35a (Rabah): If a chest holds two Kor (a Kor is about 9-15 liters), one may move it [on Shabbos]. If it holds three Kor, one may not move it.

(Rav Yosef): Even if it holds three Kor, one may move it. If it holds four Kor, one may not move it.

Abaye: A case occurred, and I asked Rabah. He forbade moving even a chest of two Korim.

This ruling is like the following Tana;

(Mishnah): The following are Tehorim, even if they have bottoms, if they hold 40 Sa'im of wet measure, which is like two Kor of dry measure (it can be piled above the top) -- a chest of straw or reeds, and a water pit in a big ship.

45b (Reish Lakish): One may move a Menorah that can be held in one hand, but not one that requires two hands;

(R. Yochanan): One may move a [used] Ner, like R. Shimon, but not a Menorah, whether it is held in one or two hands;

Question: What is the reason?

Answer #1 (Rabah and Rav Yosef): This is because a person fixes a place for it.

Question (Abaye): A person fixes a place for Kilas Chasanim (a canopy over a bed. It is supported on a beam in the middle and slopes down on both sides), yet Shmuel permits spreading the covering or taking it down on Shabbos!

Answer #2 (Abaye): Reish Lakish and R. Yochanan discuss a Menorah composed of rings. (It is prone to come apart. If one reassembles it, he makes a Kli.)

121b (R. Aba bar Kahana): Candlesticks of Rebbi's house may be moved on Shabbos.

Question (R. Zeira): Is this only if they can be moved with one hand, or even if they require two hands?

Answer (R. Aba): They are like those of your father's house.

(R. Aba bar Kahana): Wagons of Rebbi's house may be moved on Shabbos.

Question (R. Zeira): Is this only if one person can move them, or even if they require two?

Answer (R. Aba): They are like those of your father's house.

123b (Abaye): At first they permitted only Kelim that can be moved with one hand... until they permitted all Kelim, even those that require two.

(Rava): At first they permitted only Kelim that can be moved with one person ... until they permitted all Kelim, even those that require two.

Eruvin 102a: There was a beam in R. Pedas' house that required 10 people to move it [due to its weight]. They put it next to the door [to support it at night]. He did not comment;

He permitted because has Toras Kli (it is considered a Kli).

There was a mortar in Shmuel's house that contained 15 Sa'im. He let people put it next to the door, for it has Toras Kli.

Rishonim

Rambam (Hilchos Shabbos 25:6): A large rock or beam, even if 10 people are needed to move it, if it has Toras Kli, one may move it.

Magid Mishneh: The Meforshim asked that in Shabbos 35a, Rabah and Rav Yosef argue about whether one may move a chest that holds three Kor, but all forbid one that holds four Kor. Tosfos (102a DH ha'Hu) answered that one does not normally move a chest, therefore if it is very big one may not move it on Shabbos. People constantly move beams to close the door. Therefore even on Shabbos one may move it, for it has Toras Kli. The Rif and Rambam did not mention this at all. It seems that they hold that there is no source for Rabah and Rav Yosef. They were merely stringent about Tiltul. The Halachah does not follow them. This is primary.

Rambam (26:11): One may not move a Menorah composed of rings, whether it is big or small, lest he reassemble it. If it has grooves and looks like it has rings, if it is big and it is held in two hands, one may not move it, due to its weight. If it was smaller than this, one may move it.

Kesef Mishneh: This is difficult. The Gemara connotes that R. Yochanan forbids a Menorah with grooves not due to Muktzeh, rather, he decrees due to a Menorah of rings. If so, he should forbid even a small Menorah with grooves, like R. Yochanan! Also, Rabah and Rav Yosef forbid due to its weight, for a person fixes a place for it. This reason was rejected! Rather, if a big Menorah has grooves we decree due to a Menorah of rings. We do not decree about a small Menorah.

Ritva (46a DH u'Mar): [Reish Lakish holds that] it is not normal to bang a small Menorah of rings [so it will be tight and stay assembled]. We do not decree about a small Menorah with grooves due to a small Menorah of rings, for this would be like a decree on a decree [lest one permit a small Menorah of rings, and come to bang]. R. Yochanan holds that this is all one decree.

Kesef Mishneh: It seems that the Rambam rules like Reish Lakish, for he explains like Rashi, that R. Aba permits only small ones, but forbids what requires two hands. The Rambam understands that it is forbidden due to its weight, and not due to the grooves, just like wagons, which were taught right after this. We must distinguish a Menorah and wagon from R. Pedas' beam and Shmuel's mortar. They were permitted, for they have Toras Kli. The Rambam permits them above! Since the Rambam forbids due to weight, he should forbid even without grooves! Perhaps this is true, and he mentioned grooves to permit a small Menorah even if it has grooves.

Shinuy Nuscha'os (in Frankel Rambam): Most original texts of the Rambam do not say 'due to its weight.' This answers the Kesef Mishneh's question.

Tosfos (35a DH v'Afilu): The Halachah does not follow Rabah and Rav Yosef. Weight is not Mevatel Toras Kli. We find that that one may move a beam, even if it is very big, for it has Toras Kli. We find on 45b that Abaye did not accept from Rabah and Rav Yosef. He found a different reason to forbid. On 121b, we permit moving candlesticks of Rebbi's house. They are big. This is unlike Rashi and R. Chananel, who say that they are small. It is clear from 46a that all permit Menoros without grooves. They are [just like] big candlesticks!

Poskim

Shulchan Aruch (OC 308:2): Any Kli, even if it is very big or heavy, does not lose Toras Kli due to its size or weight.

Beis Yosef (DH v'Chol): The Rif and Rosh (Shabbos 49b and 17:10) bring the Heter to move the giant beam in R. Pedas' house and the giant mortar in Shmuel's house.

Bach (3): The beam has Toras Kli, for it is proper to sit on. The Tur connotes that the Halachah does not follow Rabah and Rav Yosef. Also Tosfos (35a) says so. This is unlike Tosfos Eruvin 102a, who forbids a chest because normally one does not move it during the week at all. There is no difference. Even if one does not move it during the week at all, it does not lose Toras Kli. The Beis Yosef said so, from the Magid Mishneh.

Gra (DH Kol): The Yerushalmi permits a Menorah that two people can move. If [it requires] three or five, it is forbidden. R. Ze'ira said, since one may move it, it is permitted even with four or five. This is unlike Rashi, who says that R. Aba permitted small ones [but one that requires two hands is forbidden]. According to Rashi, since we forbid one that requires two hands, why did we ask about [a wagon] that requires two people? Also, even Abaye, who is stringent on 123b, permits what one can move with two hands, and all the more so, Rava, who permits what two people can move (Hagahos Mordechai 462)!

Mishnah Berurah (8): A big rock or beam is permitted if it has Toras Kli, i.e. it is designated for use. A Kli is permitted even if one does not normally move it during the week. We do not say that due to its weight, one fixes a place for it and takes his mind off moving it. If during the week he is careful not to move it from its place, lest it get ruined, automatically it is Muktzeh Machmas Chisaron Kis, so one may not move it.

Shulchan Aruch (279:7): One may move not a Menorah, whether it is big or small, if it is composed of rings, or even if it has grooves and looks like it has rings.