Ptil Tekhelet tzitzit for Sephardic Jews
The Ptil Tekhelet Organization makes two types of strings, known as "Raavad" and "Rambam." The reason is because there is no consensus in the Rishonim as to how many of the strings should be blue and how many should be white. The Raavad strings are all blue, whereas the Rambam strings are half blue....