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Various forms of threads are used to hold parts together with reference
to each other, or to transmit power.
The 60° Sharp-V thread was originally called the United States Standard thread
, or the Sellers thread. For purposes of certain adjustments, the Sharp-V
thread is useful with the increased friction resulting from the full thread-face.
It is also used on brass pipe work.
The American National thread with flattened roots and crests is a stronger thread.
This form replaced the Sharp-V thread for general use and is still used for
existing design.
T
he Unified thread is the new standard thread agreed upon by the United States,
Canada, and Great Britain in 1948. The crest of the external thread may be flat
or rounded, and the root is rounded; otherwise the thread form is essentially
the same as the American National. The transition of industry from the
American National thread to the Unified thread for new design
has been nearly completed.
The square thread is theoretically the ideal thread for power transmission,
since its face is nearly at the right angles to the axis; but owing to the
difficulty of cutting it with dies and because of other inherent disadvantages,
such as the fact that spilit nuts will not readily disengage, the Square thread
has been displaced to a large extent by the Acme thread. The Acme thread is
not standarized.
Acme thread is a modification of the Square thread,
and has largely replaced it.
It is stronger than the Square thread, is easier to cut. and has the advantage
of easy disengagement from a split nut, as on the lead screw of a lathe.
The Whitworth thread has been the British standard and is being replaced by the
Unified thread. Its uses correspand to those of American National thread.
The Standard Worm thread is similar to the Acme thread, but is deeper.
It is used on shafts to carry power to worm wheels
The Nuckle thread is usually rolled from sheet metal but is sometimes cast, and is
used in modified forms in electric bulbs and sockets, bottle tops, etc.
The Buttress thread is designed to transmit power in one direction only, and
is used in the breech locks of large guns, in jacks, in airplane propeller hubs,
and in other mechanisms of similar requarements.
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