When tying tzitzit, you tie 7, 8, 11, then 13 krichot. I know the reason for 7 and 13 is because there are 7 shamayim in the rakiah and six passage ways between them, so there is 7 for the minimum, and 6+7 or 13 for the maximum. But what is the reason for the 8 and 11?
The 7 and 8 equal 15, like yud and hey, the first two letters of Hashem's Name. The 11 can be split into 5 and 6, like vav and hey, the last two letters of Hashem's Name. The 13 can be split into 1, 8, and 4 like alef, chet, and dalet, so it's echad. So the tzitzit mean Hashem Echad, G-d is one, and also the 13 could be for the 13 Attributes of Mercy.
Also note that Sephardim do not tie this way. They tie 5, 6, 10, 5 like yud-kay-vav-kay.