Written by Jody Muelaner
A twin nut is a type of split nut that resembles a regular hex nut cut into two pieces for quick assembly and rapid adjustment. The nut is split into two halves along a plane that passes through the axis of rotation. This allows the female thread to be opened up and placed around the male thread.
It can, then, be used to insert the nut onto a leadscrew that has no accessible end. Alternatively, it allows the nut to be opened so that it can move axially along the screw without any relative rotation — and closed at a new position so that the screw actuation can resume.
This can be useful in positioning applications, such as the leadscrew of a lathe, allowing a quick yet rough setting before accurate fine adjustments are made.
Split nuts used in these types of positioning applications are typically specially made machine parts with additional mounting interfaces where other parts of the machine or equipment are attached. They also have threads cut to match the leadscrew of the machine.
A twin nut is a special type of split nut with standard threads and a regular hex nut forms when joined
together. The two halves lock together so that it can function as a regular nut.
The ability to separate the nut and place it at an arbitrary location along a long threaded shaft can be particularly useful for clamping and tooling adjustment operations.
This term, twin nuts, is also sometimes used to refer to the combination of a jam or half nut, used with a regular
nut as a form of a friction lock nut. This is used to resist loosening under vibration and torque.
This involves tightening or “jamming” the half nut against the primary one. In this case, the jam nut should be
tightened against the part first, with the main nut then fitted over the top.