The two holes of the Tallis Katan:
Some Poskim rule that the Tzitzis is not to be tied in its classic method, in which only one hole is made by the corner, and the Tzitzis is looped through that hole. Rather the Tallis is to have two adjacent holes made by the corner and have the strings enter through one hole and exit through the other. Practically, we do not rule like this opinion, and one who decides to be stringent upon himself and follow this opinion may only do so by the Tallis Katan [and not by a Tallis Gadol].
Ruling of Siddur and practical custom: One is to make two holes by the Tallis Katan. One is to enter the strings through one hole and exit them through the second hole. One is to tie them in close proximity to the garment in order so the first knot is above 4 cm. One does not make two holes by the Tallis Gadol. [Practically, the Chabad custom follows this ruling of the Siddur, to make two holes by the Tallis Katan and a single hole by the Tallis Gadol. This is also the custom of all Chassidic Jewry. The Lithuanian and Sephardi custom is to make only one hole by both the Tallis Gadol and Katan.]
How to make the two holes: Both holes are to be both made within the legal corner dimensions [of between 4-6 cm, as explained in Halacha A]. Some people are meticulous to make these holes slightly diagonal and so is the Chabad custom.
Not to wear inside out: A Tallis Katan that has two holes in the corner is not to be worn inside out, as explained in Chapter 1 Halacha 14H!
From which side is one to tie the Tzitzis to the two-hole Tallis Katan? One is to tie the Tzitzis to the external side of the Tallis which is visible when worn. [Thus, by our Tallis Katan which is always worn with the silk corners facing the inner side, one is to make the Tzitzis on the non-silk side of the corners. See Q&A regarding Bedieved!]
Must the double hole penetrate through the back of the corner, or does it suffice for it to be made on one side?
When making a Tallis with two holes in the corner, as mentioned above, the question is asked as to whether the hole must be made through the front and back of the corner, or if it suffices to make it only by the front area of the corner. This question applies to a thick corner, or a two clothed corner [as is accustomed today to place an extra corner piece under the corner], and it is thus possible to make a hole that does not penetrate to the other side. Practically, some Poskim lean to rule that it is permitted to do so, and it is not required for the hole to exit the back end of the corner.
What is the law if one tied the Tzitzis to the back corner of the two-hole Tallis Katan?
The Tzitzis remains valid and may be worn with a blessing. This applies even if the Tzitzis of some corners were tied onto the outer corner and the Tzitzis of other corners were tied to the inner corner. Nevertheless, it is proper to undo the Tzitzis of the inner corners and replace them on the outer side of the corner, as explained above.
 Admur 11:35; M”A 11:13
 Baal Haitur Tzitzis 3 in name of Ravi
 The reason: The reason for this is opinion is because they hold that the Tzitzis may only be apparent on one side of the corner. If, however, it is apparent from both sides, then it is as if one placed 8 sets of Tzitzis and is hence invalid based on the Gemara’s teaching of “4 and not 8”. Accordingly, it is forbidden to tie the Tzitzis to a single hole. [Baal Haitur ibid; Machatzis Hashekel 11:13] The other opinions, however, argue that no such invalidation exits.
Another advantage of making two holes: A separate advantage of making two holes, in addition to suspecting for the above opinion, is that doing so ensures that the braid of the Tzitzis steadily hits the corner, as explained in 11:35. [Siddur Admur “In order so the first knot be above 4 cm”; Yeshuos Yaakov 11:5] See Chapter 4 Halacha 10A!
 Admur ibid; M”A ibid in name of Bach
The reason: In order so his stringency is not apparent to others, and he not appear like a haughty individual. [Admur ibid]
 Siddur Admur
 Sefer Haminhagim p. 7 [English]
 Birkeiy Yosef 11:5 that so was the custom of Rav Chaim Vital; Ben Ish Chaiy Noach 15 that so was custom of Arizal and Rashash; Kaf Hachaim 11:24
 M”B 11:39; See Piskeiy Teshuvos 11:21
 Siddur Admur; Ashel Avraham Butchach Tinyana 11
Other opinions: Some Poskim rule it is not necessary to make both holes specifically in the legal corner dimensions, and rather only the more inner hole, or top hole, must be within this dimension. They rule the knot is to be made on the most outer hole. [P”M 11 brought in Biur Halacha 11:9 “Yaaseh”; Chazon Ish 3:12; Implication of Poskim in Shulchan Aruch who omit the above requirement; See Piskeiy Teshuvos ibid] From here one can learn that if Bedieved by the Chabad Tallis Gadol one accidently entered the strings into both holes and made a knot, or entered the Shamash string into the side hole before making any knots, then it is valid Bedieved. Nonetheless, according to Admur ibid one should be stringent and retie the Tzitzis properly. [Shiureiy Torah p. 373; Zichronos of Rav Yaakov Landau, that so he was told by the Rebbe Rashab]
 Siddur Admur
 Siddur Admur; not found in previous sources; See Glosses of Rav Raskin footnote 86
The reason: The purpose of making it diagonal is to effect that the fringes hit within 4cm of the width of the corner, in order to follow the opinions which, require this to occur. [Siddur Admur] This means as follows: There are three parts by the corner of the Tallis, the Keren which is within 4 cm to the corner; the Kenaf which is between 4-6 cm from the corner; the Beged which is above 6 cm from the corner. [See Ateres Zekeinim 11:9] Now, since there are opinions that require the Tzitzis to hit the area called Keren, therefore one is to make the two holes diagonal so the Gdil hits within the 4 cm space of the corner. See Rav Raskin ibid
How is the diagonal made? The diagonal is made in a way that the Tzitzis bends towards the side of the corner. This is accomplished by making the two holes facing the edge of the corner, in which the top hole is the one closest to the side. [Igros Kodesh 2:313 that so was done on the Tzitzis of the Rebbe Rayatz; Likkutei Sichos 28:330; Shulchan Menachem 1:44] In Shiureiy Torah p. 270 however he writes to make the diagonal facing the middle of the Tallis like this in which the bottom hole is closes to the side. Practically, the custom follows the former view.
Other opinions: Some Poskim rule the two holes are to be made parallel to each other, like a Tzerei, and not in diagonal. [P”M 11 A”A 13; Beir Heiytiv 11:8; Ateres Zekeinim in name of Arizal, brought in Ketzos Hashulchan 6:8] The reason for this is possibly to suspect for those Poskim that rule that when the Tzitzis are hanging in a diagonal it appears like there are 8 Tzitzis, as it appears as if it is made for each side of the corner. Alternatively, it is because placing it in diagonal is a custom of the Karaits. [See M”A 11:24; See Glosses of Rav Raskin footnote 86] The holes are not to be made one on top of the other, although Bedieved it is valid even in such a case. [Chazon Ish 3:12]
 Sefer Haminhagim p. 7 [English]
 Siddur Admur which states “One must to be careful that the Tzitzis be hanging on the upper, external, part of the clothing and not on the inner lower part”; Olas Tamid 11:12; Likkutei Maharich in name of Kitzur Shlah; Arizal brought in Shaar Hakavanos Tzitzis 6; Peri Eitz Chaim Tzitzis 1; Nagid Mitzvah. “A Tallis [Katan that has two holes in the corner] is not to be worn inside out.”
The reason: As the verse states “Ureisem Oso” that the Tzitzis must be seen [Admur ibid] and when worn inside out, the inner corner blocks that area of the fringe from visibility. [See Tehila Ledavid 11:8; Ashel Avraham Butchach Tinyana 16] There is also Kabalistic reasons mentioned behind this. [Arizal ibid]
 Tehila Ledavid 11:12 “If the holes were only made on the upper part of the garment and not the lower part, it is valid”; Ashel Avraham Butchach 11 that leans to permit it; Piskeiy Teshuvos 11:26
 Tehila Ledavid 11:8; Piskeiy Teshuvos 11:21