Spring sockets may be used for the mounting of an extension spring.
You can easily adjust the spring force by screwing the socket in or out.
Spring sockets are available as standard in seven dimensions; one length of each.
If the spring socket is mounted as shown in fig. A, the spring force can easily be adjusted without disengaging the spring. Where space is limited, the spring socket can be used as shown in fig. B. Fig. C shows a spring socket used as a lever.