The Bavli, Shabas 5, amud 1, indicates that a hand is considered to be a physically large enough location that akira (lifting something from its place to transport the object) and hanacha (resting the transported object upon arrival) can be done on it, even though it's not actually large enough: the usual minimum is four tefach squared.
Later on the same page, we have:
א״ר אבין א״ר יוחנן הכניס ידו לתוך חצר חבירו וקיבל מי גשמים והוציא חייב מתקיף לה ר׳ זירא מה לי הטעינו חבירו מה לי הטעינו שמים איהו לא עביד עקירה לא תימא קיבל אלא קלט והא בעינן עקירה מעל גבי מקום ד׳ וליכא
- Rabbi Avin said that Rabbi Yochanan said: "If he brought his hand into his fellow's courtyard, caught rainwater, and took it out [to a public thoroughfare], he's liable."
- Rabbi Zera fumed at that: "What's the difference whether his fellow loaded him up [where the one whose hand is loaded up is not liable because his fellow did akira] or the sky did? He didn't do akira!"
- Rather, say not "caught" but "incorporated" [that the descending flow hit his one hand and he caught it in the other —Rashi].
- But [that can't be:] we need akira from a four-tefach surface and don't have it!
Why not? We said a hand is large enough for akira and hanacha, further up the same page. (M'iri mentions this question but doesn't answer it except to say that considering this case akira and hanacha would mean any passage from hand to hand would count as akira and hanacha also, which is impossible. But I don't see why that's impossible. It seems to fit exactly with the passage further up the page.)