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Micrometer screw
(gcide) | Screw \Screw\ (skr[udd]), n. [OE. scrue, OF. escroue, escroe,
female screw, F. ['e]crou, L. scrobis a ditch, trench, in
LL., the hole made by swine in rooting; cf. D. schroef a
screw, G. schraube, Icel. skr[=u]fa.]
1. A cylinder, or a cylindrical perforation, having a
continuous rib, called the thread, winding round it
spirally at a constant inclination, so as to leave a
continuous spiral groove between one turn and the next, --
used chiefly for producing, when revolved, motion or
pressure in the direction of its axis, by the sliding of
the threads of the cylinder in the grooves between the
threads of the perforation adapted to it, the former being
distinguished as the external, or male screw, or, more
usually the screw; the latter as the internal, or female
screw, or, more usually, the nut.
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Note: The screw, as a mechanical power, is a modification of
the inclined plane, and may be regarded as a
right-angled triangle wrapped round a cylinder, the
hypotenuse of the marking the spiral thread of the
screw, its base equaling the circumference of the
cylinder, and its height the pitch of the thread.
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2. Specifically, a kind of nail with a spiral thread and a
head with a nick to receive the end of the screw-driver.
Screws are much used to hold together pieces of wood or to
fasten something; -- called also wood screws, and {screw
nails}. See also Screw bolt, below.
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3. Anything shaped or acting like a screw; esp., a form of
wheel for propelling steam vessels. It is placed at the
stern, and furnished with blades having helicoidal
surfaces to act against the water in the manner of a
screw. See Screw propeller, below.
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4. A steam vesel propelled by a screw instead of wheels; a
screw steamer; a propeller.
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5. An extortioner; a sharp bargainer; a skinflint; a niggard.
--Thackeray.
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6. An instructor who examines with great or unnecessary
severity; also, a searching or strict examination of a
student by an instructor. [Cant, American Colleges]
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7. A small packet of tobacco. [Slang] --Mayhew.
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8. An unsound or worn-out horse, useful as a hack, and
commonly of good appearance. --Ld. Lytton.
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9. (Math.) A straight line in space with which a definite
linear magnitude termed the pitch is associated (cf. 5th
Pitch, 10
(b) ). It is used to express the displacement of a rigid
body, which may always be made to consist of a
rotation about an axis combined with a translation
parallel to that axis.
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10. (Zool.) An amphipod crustacean; as, the skeleton screw
(Caprella). See Sand screw, under Sand.
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Archimedes screw, Compound screw, Foot screw, etc. See
under Archimedes, Compound, Foot, etc.
A screw loose, something out of order, so that work is not
done smoothly; as, there is a screw loose somewhere. --H.
Martineau.
Endless screw, or perpetual screw, a screw used to give
motion to a toothed wheel by the action of its threads
between the teeth of the wheel; -- called also a worm.
Lag screw. See under Lag.
Micrometer screw, a screw with fine threads, used for the
measurement of very small spaces.
Right and left screw, a screw having threads upon the
opposite ends which wind in opposite directions.
Screw alley. See Shaft alley, under Shaft.
Screw bean. (Bot.)
(a) The curious spirally coiled pod of a leguminous tree
(Prosopis pubescens) growing from Texas to
California. It is used for fodder, and ground into
meal by the Indians.
(b) The tree itself. Its heavy hard wood is used for
fuel, for fencing, and for railroad ties.
Screw bolt, a bolt having a screw thread on its shank, in
distinction from a key bolt. See 1st Bolt, 3.
Screw box, a device, resembling a die, for cutting the
thread on a wooden screw.
Screw dock. See under Dock.
Screw engine, a marine engine for driving a screw
propeller.
Screw gear. See Spiral gear, under Spiral.
Screw jack. Same as Jackscrew.
Screw key, a wrench for turning a screw or nut; a spanner
wrench.
Screw machine.
(a) One of a series of machines employed in the
manufacture of wood screws.
(b) A machine tool resembling a lathe, having a number of
cutting tools that can be caused to act on the work
successively, for making screws and other turned
pieces from metal rods.
Screw pine (Bot.), any plant of the endogenous genus
Pandanus, of which there are about fifty species,
natives of tropical lands from Africa to Polynesia; --
named from the spiral arrangement of the pineapple-like
leaves.
Screw plate, a device for cutting threads on small screws,
consisting of a thin steel plate having a series of
perforations with internal screws forming dies.
Screw press, a press in which pressure is exerted by means
of a screw.
Screw propeller, a screw or spiral bladed wheel, used in
the propulsion of steam vessels; also, a steam vessel
propelled by a screw.
Screw shell (Zool.), a long, slender, spiral gastropod
shell, especially of the genus Turritella and allied
genera. See Turritella.
Screw steamer, a steamship propelled by a screw.
Screw thread, the spiral rib which forms a screw.
Screw stone (Paleon.), the fossil stem of an encrinite.
Screw tree (Bot.), any plant of the genus Helicteres,
consisting of about thirty species of tropical shrubs,
with simple leaves and spirally twisted, five-celled
capsules; -- also called twisted-horn, and twisty.
Screw valve, a stop valve which is opened or closed by a
screw.
Screw worm (Zool.), the larva of an American fly
(Compsomyia macellaria), allied to the blowflies, which
sometimes deposits its eggs in the nostrils, or about
wounds, in man and other animals, with fatal results.
Screw wrench.
(a) A wrench for turning a screw.
(b) A wrench with an adjustable jaw that is moved by a
screw.
To put the screws on or To put the screw on, to use
pressure upon, as for the purpose of extortion; to coerce.
To put under the screw or To put under the screws, to
subject to pressure; to force.
Wood screw, a metal screw with a sharp thread of coarse
pitch, adapted to holding fast in wood. See Illust. of
Wood screw, under Wood.
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Micrometer screw
(gcide) | Micrometer \Mi*crom"e*ter\, n. [Micro- + -meter: cf. F.
microm[`e]tre.]
An instrument, used with a telescope or microscope, for
measuring minute distances, or the apparent diameters of
objects which subtend minute angles. The measurement given
directly is that of the image of the object formed at the
focus of the object glass.
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Circular micrometer, or Ring micrometer, a metallic ring
fixed in the focus of the object glass of a telescope, and
used to determine differences of right ascension and
declination between stars by observations of the times at
which the stars cross the inner or outer periphery of the
ring.
Double image micrometer, a micrometer in which two images
of an object are formed in the field, usually by the two
halves of a bisected lens which are movable along their
line of section by a screw, and distances are determined
by the number of screw revolutions necessary to bring the
points to be measured into optical coincidence. When the
two images are formed by a bisected object glass, it is
called a divided-object-glass micrometer, and when the
instrument is large and equatorially mounted, it is known
as a heliometer.
Double refraction micrometer, a species of double image
micrometer, in which the two images are formed by the
double refraction of rock crystal.
Filar micrometer, or Bifilar micrometer. See under
Bifilar.
Micrometer caliper or Micrometer gauge (Mech.), a caliper
or gauge with a micrometer screw, for measuring dimensions
with great accuracy.
Micrometer head, the head of a micrometer screw.
Micrometer microscope, a compound microscope combined with
a filar micrometer, used chiefly for reading and
subdividing the divisions of large astronomical and
geodetical instruments.
Micrometer screw, a screw with a graduated head used in
some forms of micrometers; turning the head one full
revolution advances the position of the tip of the screw
only by a little.
Position micrometer. See under Position.
Scale micrometer, or Linear micrometer, a minute and very
delicately graduated scale of equal parts used in the
field of a telescope or microscope, for measuring
distances by direct comparison.
[1913 Webster] Micrometric |
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