Reference for Menachot 70:6
רבה קטר להו ופשיט ושדי להו רב אחא בר יעקב קטר להו ומתלית להו מר בריה דרבנא עביד כדידן
R'Aha B'Jacob used to tie the knot and then plait [the straps] together. Mar the son of Rabina used to do according to our custom.<span class="x" onmousemove="('comment',' I.e., he used to let the straps hang down over his shoulders in front.');"><sup>10</sup></span> R'Judah the son of R'Samuel B'Shilath said in the name of Rab, The knot<span class="x" onmousemove="('comment',' I.e., the special shape of the knot of the head-tefillah which must resemble the letter daleth and of the hand-tefillah which must resemble the hsa letter yod. These two letters, together with the letter shin that is embossed on the sides of the head-tefillah, form the Name , Almighty.');"><sup>11</sup></span>