Do we know what the Techeilis is - Is it the murex or the cuttlefish? Are you obligated to wear it because of Safek? 

with Hagaon Rav Shmuel Kamenetsky - Rosh Yeshiva of Philadelphia – 20:10 with Hagaon Rav Menachem Mendel Shafran - Av Beis Din Hayashar V'hatov Yerushalayim, Rosh Yeshiva Noam Hatorah Bnei Brak – 20:34 with Hagaon Rav Dovid Cohen - Rov of Gvul Yaavetz, Renowned Posek, Mechaber seforim – 21:30 with Hagaon Rav Herschel Schachter - Rosh Yeshiva & Rosh Kollel YU, Leading Posek of OU –   25:10 with Hagaon Rav Nissin Kaplan - Maggid Shiur, Mir Yerushalayim – 28:26 with Hagaon Rav David Yosef - Rosh Kollel Yachveh Da'at Kollel, Chief Rabbi of Har Nof, Member Moetzet Chachmei HaTorah – 34:57 with Rabbi Bentzion Halberstam, Rav of Khal Chassidim Westgate – 36:03 with Hagaon Rav Moshe Heineman – Rov of Agudas Yisroel Baltimore, Renowned Poseik – 55:40 with Rabbi Michoel Shlomo Bar-Ron – Founder Torath Moshe learning center – 1:11:54

מראי מקומות