I have a question regarding THREE.js.

I want to choose a specific surface from a box and then use it to detect a collision with a ball. The question is that I don't know how to choose that face. I have checked all the methods from three.js and none of them is useful. I am not sure whether there is another way to choose a specific face.

Surface and Ball

const hand1geo = new THREE.BoxGeometry(2, 0.01, 0.2);
const material_sidehand = new THREE.MeshBasicMaterial({ color: 0x3cc1b7 });
const sidehand = new THREE.Mesh(hand1geo, material_sidehand);

Above is how I created the box.