The 4B - Tackle blocks are small pulleys equipped with a quick coupling device.
They are mainly used for the return of textile ropes or, only some models and more rarely, for wire ropes.
Due to the small diameter of the pulleys, which allows only a low ratio with the rope diameter, they are intended exclusively for manual maneuvers and light loads.
In scenography they are often used, together with other devices, to carry out the manual maneuvers of:
Swag curtains Fly and swag curtains Rearward lifting curtains Frontward lifting curtains Roman curtains Venetian curtains Austrian curtains sometimes even of large dimensions but of low weight.
The cases in which they are used in the construction of simple machines that exploit the principle of mechanical advantage are an exception.