Reference for Rosh Hashanah 3:6
שׁוֹפָר שֶׁנִּסְדַּק וְדִבְּקוֹ, פָּסוּל. דִּבֵּק שִׁבְרֵי שׁוֹפָרוֹת, פָּסוּל. נִקַּב וּסְתָמוֹ, אִם מְעַכֵּב אֶת הַתְּקִיעָה, פָּסוּל. וְאִם לָאו, כָּשֵׁר:
If a shofar split, and it were glued together, it is pasul (unfit), [being like two shofroth. This, if it were split along its length. But if it were split in its width — if there remained from the mouth site until the place of the split enough (intact shofar) for blowing, it is kasher; if not, it is pasul. And how much is the amount required for blowing? (Enough intact shofar) so that if he holds it in his hand it is visible on either side.] If he glued together pieces of shofroth, it is pasul. If it were punctured and he closed it — if the blowing is impeded, it is pasul; if not, it is kasher. [This, only if he closed it with its own matter, if most of it were whole, and if the filled punctures did not impede the blowing. But if one of these conditions is lacking, it is pasul.]