Reference for Bava Batra 178:2
א"ר מני בר פטיש כדרך שאמרו לענין איסורן כך אמרו לענין טומאתן
of a shopkeeper's, and of producers' balances [which may be subjected to the laws of Levitical defilement, must be] one handbreadth! [And, since this restriction<span class="x" onmousemove="('comment',' Requiring a distance of a handbreadth from above in the case of shopkeepers' and producers' balances. ');"><sup>5</sup></span> has specifically been applied to one kind of balance, are not the other kinds of balance to be implied?]<span class="x" onmousemove="('comment',' What, then, is the purpose of R. Mani's statement? ');"><sup>6</sup></span> — [The statement of R. Mani] is required [on account of the sizes of] the beam and the cords, which have not been mentioned [there]. Our Rabbis taught: Weights must not be made either of tin or of lead or of gasitron<span class="x" onmousemove="('comment',' A fusion of different metals. Others compare the word with [G], tin; perhaps of a special kind. ');"><sup>7</sup></span>