This task is about translating a given Spanish language sentence to English.

Esta va a ser la ranura que separe la cubierta del lomo y el inicio del cartón, en realidad, cada libro va a tener su propio tamaño en esa parte, pero una regla de oro es dejar entre cuatro y siete milímetros, o es lo que generalmente se deja.
This is going to be the groove that separates the cover of the spine and the start of the board, and each book is going to have its own size of its shoulder, but a good rule of thumb is anywhere from four to seven millimeters will be fine or is where it's usually going to be.