Bava Batra 89B

אמר רב פפא: דיגרומי.

Rav Pappa says: It is a balance scale for blacksmiths, who weigh heavy pieces of metal.

אמר רבי מני בר פטיש: כדרך שאמרו לענין איסורן, כך אמרו לענין טומאתן.

R' Mani Bar Pattish says: Just as the rabbis said with regard to the prohibition of the scales that one may not use a scale that does not meet the criteria listed in the baraita, so too they said that this applies with regard to their ritual impurity. In other words, if the cords and pole are not attached in the proper manner, they are not susceptible to ritual impurity as part of the scale.

מאי קא משמע לן? תנינא: חוט מאזנים של חנוני ושל בעלי בתים ⁠– טפח! קנה ומתנא שלה איצטריכא ליה, דלא תנן.

The Talmud asks: What is this statement teaching us? We learned in a Mishnah (Kelim 29:5): With regard to the rope from which the scales are suspended, if the balance scale belongs to a storekeeper or to homeowners it must be one handbreadth in length for it to be susceptible to ritual impurity. Why, then, is the statement of R' Mani Bar Pattish necessary? The Talmud answers: Although the Mishnah in tractate Kelim discusses the rope from which the scales are suspended, it was still necessary for R' Mani Bar Pattish to mention the halakha with regard to the scale’s lever and cord, which we did not learn about in that Mishnah.

תנו רבנן: אין עושין משקלות ⁠– לא של בעץ, ולא של אבר, ולא של גיסטרון, ולא של שאר מיני מתכות. אבל עושה הוא של צונמא ושל זכוכית.

§ A baraita states: One may not prepare weights of tin [ba’atz], nor of lead, nor of a metal alloy [gisteron], nor of any other types of metal, because all of these deteriorate over time and the buyer will ultimately pay for more merchandise than he receives. But one may prepare weights of hard rock and of glass.