When you set out to buy techelet tzitzit, the first question is which kind: Rambam, Raavad or Tosafot? For those of you who are unclear on the question, when you buy a set of Ptil Tekhelet tzitzit strings, you have to select either Rambam or Raavad.
- Rambam – three all-white strings and one half-white half/half-blue string for each corner
- Raavad – three all-white tzitzit strings and one all-blue tzitzit strings for each corner
This means once tied, with Rambam techelet you will see seven white strings and one blue string hanging down from each corner, whereas with Raavad techelet you will see six white strings and one blue string hanging down from each corner.
The Rambam techelet set is use to tie according to the Rambam, of course, and also according to the Arizal. The Raavad techelet is used to tie tzitzit according to the Raavad, of course, and also according to the Vilna Gaon (a.k.a. the Gra), Sefer HaChinuch and others.
What about the Tosafot? The Tosafot calls for two techelet strings and two white strings on each corner. Most of the Rishonim hold like the Tosafos, therefore some Ashkenazim choose this approach (Sephardim and of course Yemenites generally follow the Rambam on this). Why don’t more Ashkenazim tie techelet according to the Tosafos? One reason might be found in a responsa written by HaRav Moshe Mordechai Carp in 5772, where he notes that you cannot use a techelet string in place of white, therefore if halacha is not like the Tosafot, you would have too many techelet strings in your tzitzit.
For those who do follow the Tosafot, Ptil Tekhelet used to make a “Tosafot” set, but now you have to simply buy two sets of Raavad (or one set of regular Raavad and one set of Raavad 7). Or if you have us do the tying, we recently introduced a Tosefot option for our tallis katan products and can tie it on a tallis gadol by request.