Gemara

18a (Mishnah): One is Mo'el in he or she wore a tight necklace (of Hekdesh), or a ring, or drank from a gold cup.

19a: The Torah equates Me'ilah to Sotah;

A Sotah is called Mo'eles even without Pegam. We learn that also Me'ilah applies without Pegam, e.g. wearing a Hekdesh ring;

Bava Metzi'a 69b: Rav Chama used to rent a Zuz for an eighth of a Zuz per day. He lost all his money.

He reasoned that one may rent them, just like one may rent a shovel!

Rejection: A shovel is different, for one returns the same shovel itself, and its depreciation is not known. One does not return the same coins, and their depreciation is known.

Rishonim

Rif (Bava Metzi'a 41a): A shovel is different, for one returns the same shovel itself. One does not return the same coins. Even if he would return the same coins, a shovel's depreciation is known, but coins' depreciation is not known.

Rebuttal (Rosh Bava Metzi'a 5:46): The Rif's text is wrong. It connotes that even if one rented coins not to spend them, rather, to return the same coins, one may not charge rental. This is wrong. A Tosefta permits renting coins to a moneychanger for him to appear with them, learn from them or become rich through them! If one did so with Hekdesh he was Mo'el. The Rivan's text did not mention depreciation. Some texts mention it. One explains them as follows. The same shovel is returned, and one may not use it for any desire and return another. Even so, it would be permitted to take rental for it. One may not learn from it to coins. The rental (paid for a shovel) is not for the lending, i.e. permission to do anything with it and return another. Rather, it is because the owner accepts the depreciation if the borrower will return the same one. This does not apply to coins.

Rambam (Hilchos Malveh 5:16): One may not rent coins. This is unlike renting a Kli. The same Kli itself is returned, but one who borrows coins spends them and returns other coins. Therefore, it is Avak Ribis.

Rambam (8:11): One may rent a copper pot for rental, even if the renter pays also for the decrease in weight.

Kesef Mishneh: The Gemara answered that if he pays for the decrease in weight, he may not take rental, for it is Ribis! It answered that the renter does not pay for the decreased value, therefore it is not Ribis.

Tosfos (69b DH Oger): R. Chama used to accept Acharayus for Ones, therefore he thought that he may charge rental.

Tosfos (69b DH Mara): Rashi explains that the same shovel is returned, and its depreciation is known, i.e. it is recognized if it depreciated from usage. A borrower does not return the same coins, for he spends them. Therefore, the Acharayus is on him, and the rental is Ribis, even if he called it rental. Further, even if he returned the same coins, their depreciation is not known. Therefore, there was no reason for the wages; they are Ribis.

Question (Tosfos and Mordechai Bava Metzi'a 437): This is astounding. Does Ribis apply to rental of a ring to wear or a cup to drink from?! There is Me'ilah for these for benefit without depreciation! A Tosefta permits renting coins to a moneychanger for him to adorn himself (some texts - appear) with them!

Answer #1 (Tosfos): The Rivan's text did not mention depreciation. It seems that the text should mention it. A Shovel is not a Halva'ah, for one may not use it for any desire and return another. Rather, one must return the same shovel. The rental is not for the lending. Even if one would lend it for any desire and return another, it would be permitted to take rental for it. One may not learn from it to coins. The rental is not for the lending, i.e. permission to do anything with it and return another. Rather, it is because the owner accepts the depreciation if the borrower will return the same one. This does not apply to coins. R. Chama rented coins for spending them, and not for accepting depreciation.

Answer #2 (Mordechai): Really, the Gemara answered that one expects to return the same shovel. This reason alone suffices to rent it, even if it does not normally depreciate. Even if one rented it to do his desires and return another, this is not Ribis, for the rental is to exempt himself from paying the depreciation if he will return the same shovel. It is not normal to borrow and return the same coins. Also, they do not readily depreciate. One pays back good coins. The rental is not for accepting any depreciation. The Ri's text omits 'their depreciation is not known.' One may rent a ring or cup because they themselves will be returned. There is more reason to permit regarding a shovel or boat.

Terumas ha'Deshen (302): It is better not to find ways to permit lending with Ribis. Even so, I will present the Halachah. A Gilyon (marginal note) in Tosfos in Bava Metzi'a says that if the lender has all the Acharayus, he may fix a rental. This is not a loan, rather, a deposit. He receives rental of his coins. Tosfos permits renting money to a moneychanger, because he returns the same coins. The same applies if he rented them to spend them, since the lender has all the Acharayus. R. Tam said so. Tosfos says that R. Chama accepted Acharayus for Ones. It seems that had he accepted all the Acharayus, it would be permitted. Maharam connotes like this. The Or Zaru'a says that R. Chama accepted Acharayus for theft or loss. It seems that if not (i.e. had he accepted even for Ones), it would be permitted. However, the end of Teshuvas Maharam connotes that the only Heter is if he gives the money for a gift, which the recipient can return. This implies that acceptance of all Acharayus would not suffice. However, perhaps Maharam gave a better counsel, for through a gift the giver need not accept Acharayus, and the recipient will guard it well. I say that for a proper Heter, the lender should accept Acharayus even for negligence, unless it is negligence that is like overt damage.

Poskim

Shulchan Aruch (YD 176:1): One may not rent coins, i.e. I will rent to you 10 Zuzim for a Zuz per month. This is when he rents them to spend them. If he rents them in order to learn from them or appear with them, and he will return the same coins, it is permitted.

Beis Yosef (DH ba'Meh): According to the Rif and Rashi, one may not rent coins even for the sake of learning or to appear with the coins. We do not rely on the Tosefta, because the Gemara disagrees. Sefer ha'Terumah holds like the Rambam, but only if he is like a regular renter; he is liable for theft or loss, and the owner loses if there is Ones. The Mordechai says that if he spent the money, he may not pay (rental), due to Ribis. Surely he discusses when he initially took the money to learn or appear with it. If he borrowed it to spend it, it is forbidden (to return more than he received) even if he did not spend them. Since a loan is for spending, once he gets it, it is as if he spent it.

Taz (1): Even if he returns the same coins, since he was allowed to spend them and the borrower had Acharayus, it is a loan. Regarding Kelim, the rental is for depreciation. Tosfos says that therefore, if one lent gold or silver Kelim like a loan and the borrower has Acharayus, one may not take rental for it, just like a loan of coins.

Gra (1): The Tosefta permits renting coins to a moneychanger for him to appear with them... when the moneychanger is liable for theft or loss, but not Ones. He is (liable) like a Shomer Sachar. If Nishtalshu, i.e. he has a third liability, i.e. Ones, it is forbidden due to Ribis.

Rema: This is only if he accepted Acharayus only for theft or loss. If he accepted all Acharayus, it is forbidden. If the owner accepted all Acharayus, for theft, loss or Ones, some permit even if the renter will spend them. However, if the owner accepted Acharayus only for theft or loss but not Ones, or only for Ones but not for theft or loss, he may not spend them for due to paying rental for them. If the owner did not accept any Acharayus, it is full Ribis.

Beis Yosef (DH Asur): The Rivash (305) says that surely R. Chama transgressed Ribis mid'Oraisa, since it was a proper loan, just he called it a rental. However, if so, (R. Chama thought that) there is no Ribis! (Anyone can call it a rental!) Rather, Tosfos explains that R. Chama exempted the borrower from any Ones that would occur before he spent them, like a renter. Therefore, it was only Avak Ribis. The Rambam says that it was Avak Ribis. Presumably, he holds like Tosfos.

Shach (2): The Beis Yosef said that even though the Terumas ha'Deshen permits, he said t one should not do so. Really, the Terumas ha'Deshen said so only when the borrower promises and stipulates not to be believed to say that the principal was lost or stolen or Ones occurred, only if the Shali'ach Tzibur and Gabai will testify. If he does not stipulate, surely it is permitted!

Gra (2): The Terumas ha'Deshen permits when the owner takes all Acharayus, even if the borrower is authorized to spend them. HE needed to say that Tosfos discusses when he did not accept all the Acharayus. This is very difficult. All the Poskim forbid whenever the borrower is authorized to spend them.

Shulchan Aruch (2): One may rent Kelim, even if the owner gave permission to sell them or do all his desires, as long as in the end he returns a similar Kli.

Beis Yosef (DH v'Kelim): This is like Tosfos and the Rosh.