Rashi on Exodus 38:24/רש"י על שמות ל״ח:כ״ד

1ככר [TWENTY NINE] TALENTS — A common kikkar contains sixty common manehs, and the maneh of the Sanctuary (that used for purposes connected with the Temple) was double the common maneh. Consequently the kikkar here mentioned was 120 common manehs. Now a common maneh contained 25 Sela’im (or shekels), and the kikkar of the Sanctuary equals three thousand shekels. That is why Scripture counts (mentions the number of) all the shekels that are fewer than 3,000 as a separate item, because these do not together amount to a kikkar (cf. Bekhorot 5a).