How does the reusable holdback bar work?
Source: YouTube

The bar is placed between a tong-like (two hooks) device on the aircraft, and when released, the body of the holdback bar envelops the hooks (note the disappearing red paint on the tips of the hooks) forming a collet.



On the inside, as the plane pulls on the bar (1), the walls (2) compress a chamber filled with hydraulic fluid (3). The fluid pushes into a channel and pushes against a sphere (4). At the right pulling force, the sphere is pushed which allows the fluid to fire the piston (5) freeing the inserted hooks from the bar.


Source: YouTube



Reference: Repeatable release holdback bar, US Navy patent US4101099A