The advantage of a double or triple thread over a single is that you develop more travel per rotation while maintaining large thread surface area. You will often find double/triple threads in linear actuators and CNC machines because it increases the rate of travel for a given rpm while maintaining thread strength.
when lead of the screw is equal to the pitch it is called single threaded screw
screw thread are single threads which means they are not double
The IMA (ideal mechanical advantage) of a screw is determined by the ratio of the circumference of the screw head to the pitch of the screw thread. The formula for calculating IMA is 2πr/p, where r is the radius of the screw head and p is the pitch of the screw thread.
The mechanical advantage of a screw is determined by comparing the distance traveled along the screw's threads to the force applied to turn the screw. It is calculated as the ratio of the circumference of the screw to the pitch of the screw thread. A higher mechanical advantage indicates that less force is needed to lift a load.
The ANSI B1.11 Microscope Objective Screw Threads standard covers the single screw thread size: 0.8000"-36 AMO. The standard lays out the screw thread parameters and the parameters for screw thread gauging. There is some mis-information published on the web related to this screw thread which is corrected at this webpage: http://www.ring-plug-thread-gages.com/ti-spec-ANSI-ASME-B1.11.htm
One
The angle of a thread of a screw is an angle between the threads and it is the defining factor for the shape of the screw thread.
A thread may be either right-hand or left-hand. A right-hand thread on an external member advances into an internal thread when turned clockwise; a left-hand thread advances when turned counterclockwise. If a single helical groove is cut or formed on a cylinder, it is called a single-thread screw. Should the helix angle be increased sufficiently for a second thread to be cut between the grooves of the first thread, a double thread will be formed on the screw. Double, triple, and even quadruple threads are used whenever a rapid advance is desired, as on valves.Pitch and major diameter designate a thread. Lead is the distance advanced parallel to the axis when the screw is turned one revolution. For a single thread, lead is equal to the pitch; for a double thread, lead is twice the pitch. For a straight thread, the pitch diameter is the diameter of an imaginary coaxial cylinder that would cut the thread forms at a height where the width of the thread and groove would be equal.Thread forms have been developed to satisfy particular requirements. Where strength is required for the transmission of power and motion, a thread having faces that are more nearly perpendicular to the axis is preferred. These threads, with their strong thread sections, transmit power nearly parallel to the axis of the screw. (Sci-Tech Encyclopedia)For the source and more detailed information concerning your request, click on the related links section (Answers.com) indicated directly below this answer section.
By 'single threaded' you really mean single start thread. So there is just one continuous thread running up the screw. Double start thread means that two threads start from the point and run up the screw entwined with each other. For the same thread spacing the double start will screw into the wood twice as quick but require more torque to drive it. Double or Twin start often used with power screwdrivers.
it is what allows the screw to grip into the material its being screwed into. a screw without a thread is a nail
in case of simple screw jack it's single start square thread in case of worm geared screw jack it's double start square thread double start gives greater speed but requires more torque ,hence worm geared :)
A thread may be either right-hand or left-hand. A right-hand thread on an external member advances into an internal thread when turned clockwise; a left-hand thread advances when turned counterclockwise. If a single helical groove is cut or formed on a cylinder, it is called a single-thread screw. Should the helix angle be increased sufficiently for a second thread to be cut between the grooves of the first thread, a double thread will be formed on the screw. Double, triple, and even quadruple threads are used whenever a rapid advance is desired, as on valves.Pitch and major diameter designate a thread. Lead is the distance advanced parallel to the axis when the screw is turned one revolution. For a single thread, lead is equal to the pitch; for a double thread, lead is twice the pitch. For a straight thread, the pitch diameter is the diameter of an imaginary coaxial cylinder that would cut the thread forms at a height where the width of the thread and groove would be equal.Thread forms have been developed to satisfy particular requirements. Where strength is required for the transmission of power and motion, a thread having faces that are more nearly perpendicular to the axis is preferred. These threads, with their strong thread sections, transmit power nearly parallel to the axis of the screw. (Sci-Tech Encyclopedia)For the source and more detailed information concerning your request, click on the related links section (Answers.com) indicated directly below this answer section.