Bava Batra 14B

שברי לוחות שמונחים בארון. ואי סלקא דעתך ספר תורה הקיפו ששה טפחים; מכדי כל שיש בהקיפו שלשה טפחים ⁠– יש בו רוחב טפח, וכיון דלאמצעיתו נגלל ⁠– נפיש ליה מתרי טפחא רווחא דביני ביני; בתרי פושכי היכי יתיב?

the broken pieces of the first set of tablets, which were placed in the Ark. Having cited the baraita, the Talmud now presents its objection to what was taught earlier with regard to the dimensions of a Torah scroll: And if it should enter your mind to say, as R' Yehuda HaNasi held, that the circumference of a Torah scroll is 6 handbreadths, now since any cylindrical object having a circumference of 3 handbreadths has a diameter of one handbreadth, a Torah scroll with a circumference of 6 handbreadths has a diameter of two handbreadths. And since a Torah scroll is wound to the middle, since it is rolled from both sides, it must take up more than two handbreadths due to the space between the sheets of parchment and the double rolling. According to R' Meir, who says that the Torah scroll was placed inside the ark, how did the scroll fit in the remaining two handbreadths [pushkei] of space in the Ark?

אמר רב אחא בר יעקב: ספר עזרה לתחלתו הוא נגלל. ואכתי, תרי בתרי היכי יתיב? אמר רב אשי: דכריך ביה פורתא, וכרכיה לעיל.

Rav Aḥa bar Ya’akov said: The scroll of the Temple courtyard, which was kept in the Ark, was wound to its beginning, i.e., it had only a single pole, so that its circumference was only two handbreadths. The Talmud asks: But still, how does an item that is two handbreadths wide fit into a space that is precisely two handbreadths? It would be impossible to fit it in. Rav Ashi said: A small section of the scroll was wound separately and then placed on top of the scroll.