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To form a close-fitting thread that will not be loose afterwards, roll-forming requires a lobed tool rather than a constant diameter cylindrical tool. This is particularly the case when the tool and the fastener are the same, such as for a screw. A lobed or polygonal form allows residual compressive
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This lobular thread has other advantages too. It allows the screw to be turned with lower torque, which also increases the 'strip-to-drive ratio' between the torques needed to drive the screw in or to damagingly strip the threads out. The proportions of the lobular thread can also change over the
119:, five has better stability than three in imperfectly circular holes. More lobes than this, such as seven, would reduce the spacing for clearance between the lobes. A patent has been applied for about a thread with such an optimised pentalobular form.
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or plastics and forming their own thread. They may be either self-drilling, forming their own hole through unbroken material, or fitted into a pre-pierced hole. Self-drilling screws have some ability to cut a thread, as for a
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length of the screw, so that the tip of the screw can use greater lobulation to form the thread more aggressively and also provide a centring effect.
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Such thread forms are not a new innovation. A patent for machinery to roll-form the threads of the screws was granted in 1975.
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stresses from the forming parts of the thread to be relieved in the undercut clearance between the lobes.
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with sharp arrises, a three-lobed thread of this form is the basis of the well-known
Taptite screws.
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The difference in minimum and maximum radii has been exaggerated (doubled) for illustration.
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This article is about screw threading. For the screw head used in Apple products, see
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202:, "Method of making a thread forming screw", issued 1975-04-08
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The optimum number of lobes is five. Their number should be
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the thread, pushing excess material out of the way by
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39:maximum diameters for the formed thread.
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173:"TAPTITE PRO® Thread Rolling Fasteners"
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146:"Externally threaded fastener element"
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58:. Self-forming screws are used in
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76:are widely used for driving into
148:. Patent application 20140328646
31:pentalobular thread between the
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144:Müller, Kurt (2014-11-06).
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235:Threading (manufacturing)
48:pentalobular screw thread
18:Pentalobe security screw
104:In conjunction with a
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91:plastic deformation
74:Self-tapping screws
62:materials, such as
52:self-forming thread
230:Threaded fasteners
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27:Axial view of a
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35:minimum and
180:taptite.com
78:sheet metal
219:Categories
200:US 3875780
152:31 January
126:References
64:aluminium
54:used for
68:plastics
117:reamers
60:ductile
225:Screws
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56:screws
176:(PDF)
113:prime
187:2019
154:2015
66:and
83:tap
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