The silver bowls used for the blood management in the Beis HaMikdash are known to have had thin sides, despite this not being a requirement of the Torah. The silver basin is known to have had thick sides. How did Chazal know this to be the case, given that they had never seen them?
The Gra notes in the Gemara in Yuma that wherever the word שני – “two”, appears, a direct association is being drawn between the two articles under discussion, that they are the same. For example, the “two” goats on Yom Kippur had to be identical in appearance, height, and value, derived from the use of the word שני three times.
The Torah refers to the bowls as שניהם מלאים, implying that they were the same size. But this can’t be; the listed weight of the basin is 130, whilst the bowl weighed 70. Therefore, if the two utensils had the same volume, but the weight parameters had to be different, Chazal deduced that the solution was to make one of them thicker. Ingenious!