Is a specific size required for the pebbles used in the Rami of the Jamarat, and what are the consequences of not adhering to this size?

The throwing of the pebbles (rami al-jamarat (definition)) should be done with medium-sized pebbles, which the Prophet, peace and blessings be upon him, described as "pebbles for slinging" (hasa al-khadhf). The jurists have estimated their size to be larger than a chickpea but smaller than a hazelnut, or like a fava bean, or smaller than a fingertip. According to the Hanbalis, throwing with a very small or large pebble is not valid, whereas the majority of scholars hold that it is valid but disliked. It is recommended for the pilgrim to choose medium-sized pebbles and avoid very small or large ones, in order to avoid the disagreement of those who consider it invalid.