Buckle: getting a break above the bottom card
The Buckle is a brief sleight to create a separation above the bottom card and retain it with the pinky. Julio Ribera explains its usefulness as a preparation for other handlings: adding cards, separating a group in packet magic, or preparing a palm. Those possibilities serve as context; the lesson is dedicated to the Buckle.
Preparing the break
The explanation starts from Mechanics Grip and examines the contact points that hold the deck while pressure is applied. Julio shows the slight bend that allows you to obtain the necessary space and the transition from that bend to a break that can be maintained.
The action is repeated with the deck and with a packet to recognize the same principle in both cases. The work consists of controlling the pressure without the entire hand having to change position.
Minimizing the movement
A central part of the teaching is reducing the finger motion. Julio compares a broad execution with a more subtle one and recommends that the fingers accompany the grip naturally. The break must remain available for the subsequent action without drawing attention to its preparation.
You need an ordinary deck and a familiarity with Mechanics Grip and the concept of maintaining a break. No special props are required. It is a specific tutorial to practice a handling resource that you can incorporate into later techniques; it does not include the development of the routines mentioned as examples.