How would Abaye (on the bottom of 14a understand this statement of Beis Hillel? It seems Abaye explained the earlier Braisa that a small machteshes can be used on Y.T. for chilka and disa which seemingly are grain.
Avraham Sacks, Ramat Beit Shemesh
1) The second Mishnah in Beitzah 14b states in the name of Beis Hillel that one may not send on Yomtov a gift to a friend of Tevuah. Rashi DH Aval explains that this is because it cannot be used today because one may not grind on Yomtov. The question is how does this reconcile with Abaye, at bottom 14a, who maintains that it is only in a large mortar that one may not grind, but in a small mortar one may grind daisa, and Rashi 14a DH Tarti also writes that chilka and daisa may be ground if the labor involved is not great.
2) We can answer by noting that Rabbi Shimon, mentioned immediately after Beis Hillel in Mishnah 14b, permits sending a gift of tevuah. Rashi DH writes that this is because they may be ground in a small mortar. Tosfos Yomtov on the above Mishnah cites the Magid Mishneh on the Rambam Hilchos Yomtov 5:6, at end, who writes that the Tana Kama, who disagrees with R. Shimon and prohibits sending a gift of tevuah, takes account of the majority of people. Most people do not grind tevuah in a small mortar, even though this is in fact permitted on Yomtov.
3) The Meiri 14b DH Zehu Biur writes that some rule according to Beis Hillel. He writes that this is not because they disagree with the din of R. Shimon that one may grind tevuah in a small mortar. Rather, they only prohibit sending the tevuah as a gift because it looks as if one is sending the tevuah to be ground in a forbidden way and is doing a weekday activity.
4) So it is permitted to grind daisa and chilka in a small machteshes on Yomtov, but since most people do not grind in a small mortar, Abaye may agree with Beis Hillel that one may not send this gift on Yomtov because the onlooker will suspect that the gift is being sent to do something which is prohibited on Yomtov.