There are Tzitzit that have one hole and some have two. What is the significance of the multiple holes? Whose custom is it to have one? Whose custom is it to have two?
The Beis Yosef, in the last paragraph in Orach Chaim chapter 11, deals with this issue. The reason for 2 holes seems to be that when you put the tzitzis through 1 hole, they apply on both sides of the garment, making them 8 and not 4 and therefore pasul (reason?).
Based on the minhag around the Beis Yosef, he did not subscribe to this logic and said that wearing 2-hole tzitzis would be arrogant. Others give much weight to the 2-hole theory. Mishna Berurah, Chapter 11, paragraph 9(39), cites the Beis Yosef and others. The Mishna Berurah gives power to both minhagim that have developed, and concludes that each person should follow his community's custom. See the Mishna Berurah inside; an English translation is available online.