Gemara

If the hair was removed from the skin, there would be a hole.

Question (Rav Acha bar Yakov): If so (there are holes in hide when the hairs are removed), how can we write Tefilin? We (expound "u'Chsavtam" to) require Kesivah Tamah (a pure writing, without holes in the parchment)!

Answer: Chachamim of Eretz Yisrael taught that we are not concerned for any hole that the ink passes over.

Menachos 29a (Mishnah): Even one Kesav (letter) is Me'akev (in a Mezuzah).

Objection: This is obvious! (It says "u'Chsavtam". The Kesav must be Tam (complete)!)

Answer #1 (Rav Yehudah): The Mishnah teaches that even the Kotz (protrusion) of a Yud is Me'akev.

Objection: Also this is obvious! (Without the Kotz, the Yud is invalid.)

Answer #2 (Rav Yehudah): The Mishnah teaches that if a letter is not Mukaf Gvil (surrounded by blank parchment) on all four sides, (it and therefore) the entire Mezuzah is Pasul.

Version #1 (Ashi'an bar Nidvach citing Rav Yehudah): If there is a hole in the Toch (inside) of a 'Hei', it is Kosher. If there is a hole in the Yerech (leg), it is Pasul;

Version #2 (R. Zeira): If there is a hole in the Toch of a 'Hei', it is Kosher. If there is a hole in the Yerech, if the required size for a letter remains, it is Kosher. If not, it is Pasul.

The leg of the 'Hei' in the word "ha'Am" in the Tefilin of Agra was broken into two.

R. Aba: If the required size for a letter remains, it is Kosher. If not, it is Pasul.

Rishonim

Rambam (Hilchos Tefilin 1:19): One must be careful when writing a Sefer Torah, Tefilin or Mezuzah that two letters not touch. If a letter is not Mukaf Gvil on four sides, it is Pasul.

Rambam (20): If there are holes in the parchment, one may not write on the holes. If the ink passes over a hole, it is not considered a hole. Therefore, one may not write on tanned skin of a bird. If the parchment was punctured after it was written, if the hole is inside a letter such as Hei or Mem or other letters, it is Kosher. If the hole is in the Yerech and the letter is broken, if the size of a full small letter remains it is Kosher. If not, it is Pasul.

Rosh (Hilchos Sefer Torah 15): In one Perush, Rashi says that the left leg of a Hei is called the inside. The Yerech is the right leg. Rashi gave a second Perush, that the inside is the parchment inside. His first Perush is primary. It teaches that there is no Shi'ur for the remnant of the inner leg of a Hei. Any remnant is Kosher. According to the latter Perush, why did the Gemara discuss Hei more than other letters?

Mordechai (Hilchos Ketanos 952): In the end of Hilchos Tefilin, he (R. Shimshon) wrote that Hekef Gvil disqualifies b'Di'eved only in the letters of Hash-m's name.

Mordechai (953): Rashi says that the left leg of a 'Hei' is called the inside. It is called the inside because it hangs from it. I disagree. The inside is the air (blank parchment), like it says in Gitin (20a) 'carving out the insides (of letters).' Also, what is the difference between the right and left legs? Why is it less than the point of a Yud (which is Me'akev)? Since the Gemara gave a Shi'ur (how much must remain) regarding Yerechos, but not regarding the inside, this connotes there is no Shi'ur for the inside. If nothing remains of the leg, it is a Reish or Dalet! It is difficult to say that there is a Shi'ur, but the Gemara did not teach it. In Rashi's second Perush, the inside is the parchment inside, regarding Tefilin. What forced him to discuss specifically Tefilin? Also, why did the Gemara discuss Hei more than other letters? Perhaps it is to teach that it must be open at the bottom. However, the Yerushalmi teaches about a Beis that if there is a hole in the middle, it is Kosher only if it is Mukaf Gvil on all sides. However, the Bavli does not require Hekef Gvil. All our Rebbeyim agree about this. Also, perhaps Rashi discussed Tefilin to teach that the hole mentioned regarding Tefilin refers to the Yerech, but we are not concerned for the inside. 'Yerech' refers to the right and left. We are not concerned for any hole that the ink passes over.

Poskim

Shulchan Aruch (OC 32:15): If after one wrote a Hei or Mem (in Tefilin), the (parchment) inside was punctured, it is Kosher, even if the puncture fills the entire inside.

Gra (37): This is like Version #2 of Rashi. Sefer ha'Terumah says that this is primary. Tocho connotes the hollow inside. Version #1 is difficult. What is the difference between the right and left legs?

Gra (40): To answer the Rosh's question, Sefer ha'Terumah holds that the Gemara discussed a Hei in order to teach about the right leg.

Damesek Eliezer: This is difficult. Sefer ha'Terumah does not distinguish the legs!

Gra (38): All the Meforshim explain like this. The Gemara said Stam (that a hole in the Toch is Kosher).

Mishnah Berurah (34): Every letter must be Mukaf Gvil on four sides. If initially it had Hekef Gvil, but later it lost it due to a puncture or tear, it is Kosher (Sa'if 16). Most Poskim require Hekef Gvil only outside, but not on the inside. This is even if it never had Hekef Gvil inside. L'Chatchilah one should not write even if the hole is inside and does not fill the hollow. B'Di'eved it is Kosher, and it need not be fixed.

Mishnah Berurah (35): the same applies to all letters with three sides. If it has only two sides, e.g. a final Chaf, it is not considered to have an inside.

Mishnah Berurah (36): Even if the hole touches the letter itself, as long as a thin remnant remains it is Kosher, for there is no Shi'ur for the thickness of the letters.

Shulchan Aruch (ibid.): However, the Yerushalmi connotes that also the inside must be Mukaf Gvil.

Beis Yosef (DH u'Mah she'Chasav Rabeinu Hilkach): The Tur says that if the entire inside was punctured, it is Pasul. Perhaps this is the conclusion of the Yerushalmi's opinion. Or, it is the Tur's own opinion. I.e. he rules like the Yerushalmi, since it is Posel and it is not clear that the Bavli is Machshir. However, the Rambam is Machshir. He did not stipulate that not all of the interior was punctured.

Note: The Rambam disqualifies a letter that is not Mukaf Gvil on four sides. Perhaps he means that it must be Mukaf Gvil only externally, or that it does not touch another letter, like the Beis Yosef says below (DH v'Im).

Beis Yosef (ibid.): The Mordechai and Sefer ha'Terumah say that the Bavli is Machshir. Why did the Tur say that some Poskim say so? All the Poskim say so! We must say that it is because according to Version #1 of Rashi, the Bavli did not discuss this, so we rely on the Yerushalmi. According to Version #2, even if the entire inside is punctured, it is Kosher. Those who are Machshir hold that Version #2 is primary.

Beis Yosef (DH v'Im Tomar): How are we Machshir any letter with a hole? In Menachos, we disqualify any letters not Mukaf Gvil on four sides! I answer that this is only when it touches another letter, but not if it borders a hole. I learn from Rashi, who says 'parchment does not surround it. It clings to another letter.' Regarding a broken Vov, he says 'when writing it, the scribe encountered a hole (in the parchment).' Even so, it is Kosher if a child can read it. Alternatively, it is Kosher only if it was broken after it was written. Since initially it was Mukaf Gvil on four sides and Kosher, it is Kosher even if later it was punctured. If there was a break from the beginning, even if it has the required Shi'ur, it is Pasul, for it was never Mukaf Gvil. This is like the Rambam.

Beis Yosef (DH uvi'Teshuvas): Maharalbach (1) says that in Tefilin, often the leg of a final Chaf reaches to the bottom of the parchment. It was never Mukaf Gvil (on the bottom). I disqualified them based on some Poskim who explicitly said so. None of the Rabanan disagreed. It is not clear that the Rambam disqualifies. He did not list this among things that disqualify. He mentioned only that two letters may not touch. Hagahos Maimoniyos (200) brings that the Yerushalmi requires Hekef Gvil inside the letter, and all the more so outside the letter. If a letter is not Mukaf Gvil on four sides, it is Pasul. The Me'iri says that if it was punctured before it was written and the ink does not pass over it, it is Pasul. If it was punctured after it was written, the Gemara says that a hole in the middle of a Hei is Kosher. If the hole is in the Yerech and the letter is broken, it is Kosher only if the size of a full small letter remains. The Me'iri holds that the Rambam agrees, since he did not bring the Rambam's opinion at all. Also the Tur says so. In Gitin, when the Ramah explains that letters that touch in a Get do not disqualify, he says that if a letter in Tefilin or a Sefer Torah lacks Hekef Gvil due to a hole in the parchment, it is as if it touches a letter.

Taz (8): Version #1 in Rashi is lenient to be Machshir any remnant in the inner leg of a Hei. It is stringent about a hole in the middle. Therefore, we rely on the Yerushalmi that disqualifies. Version #2 is stringent about the inner leg, and requires that the size of a full small letter remain. It is lenient about a hole in the middle. The Rosh holds like Version #1, but the Rema brings that the other Poskim hold like Version #2. If so, we do not require Hekef Gvil inside. However, perhaps the Rema is stringent for both versions. This is proper. However, the Tur concludes 'if the entire inside is punctured, it is Pasul.' This implies that if some remains, it is Kosher.

Mishnah Berurah (37): One should be stringent like the Yerushalmi. It requires Hekef Gvil on all sides. If it was tirn before it was written, one should erase part of the thickness of the letter so it wil have Hekef Gvil.

Shulchan Aruch (ibid.): If the inner leg of the Hei became punctured, even if only Mashehu remained, it is Kosher according to the Rosh.

Mishnah Berurah (38): The Rosh is lenient only about a Hei. The remnant can be on top of the hole or below it. He agree that the left leg of other letters such as Tov is like the right leg.

Rema: The other Poskim require that the size of a full small letter remains. This is the Halachah. If the right leg of the Hei became punctured, it is Kosher only if the size of a full small letter remains.

Magen Avraham (16): A small letter is a Yud. If the thickness of a Hei was broken, if a strand remains like a thin Yud or Vov, it is Kosher.

Mishnah Berurah (44): This refers to a Yud with the Kotz at the bottom.

Mishnah Berurah (40): The Rema connotes that he holds that the Halachah Vadai follows the other Poskim.