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Questions tagged [fasteners]

82 questions
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Why exactly does a washer help distribute the stress around a bolt?

Usually the reason for having a washer under a bolt head is stated to be that it helps to evenly distribute the stress to the clamped material surface. But why is this? I would understand if the washer was significantly larger than the bolt head.…
S. Rotos
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What is this Y-shaped screwdriver bit, and what is its purpose?

I found this strange looking bit in a bit set of uncommon bits, including Security Torx, hexalobular, tri-wing, spanner head, 12-point flange, Torq-set and others. It's the only one that I could not identify, what is it for?
jms
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12
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Why are most standard bolt threads single start?

When looking at thread descriptions, one of the basic properties is always the number of thread starts. As far as I could tell, all of the major standard bolt threads are single-start. This includes: Unified Standard (UNC, etc.) National Pipe…
hazzey
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6
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3 answers

What causes a fastener to lock?

I am rebuilding a car engine. With some of the fasteners I am unscrewing, I notice that a lot of torque is required to undo the fastener. It feels like a snap when undoing a fastener, rather than a smooth twist. If I tighten the fastener to a set…
tgun926
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4 answers

Why are Whitworth threads angled at 55°?

You're probably thinking, "Well.. Why not? It's gotta be something.." Right? But 55° is kind of an odd angle if you think about it.. and it does seem like a pretty specific choice considering a perfect equilateral/equiangular triangle consists of…
voices
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How does Alloy 20 compare with Ti 6-4, C-276 and 316 stainless for corrosive service?

While I've designed tons of plastics for corrosive service, the fasteners to hold the plastics together are inevitably metallic. There have been a lot of ways to protect them from rusting (due to exposure to things like 33% HCl, 50% H2SO4, 50%…
Mark
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Origins of the "threaded fastener pullout formula"

I was looking through NASA's document for "Installation Torque Tables for Noncritical Applications" and noticed their formula for the pullout load of a fastener on a certain material. It goes as follows: $$P = \frac{\pi\cdot d_m \cdot F_s\cdot…
TwoWaySpeedOfLight
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Why can't screws be used for locating parts?

I remember hearing awhile back that it's not a good idea to use screws to locate/align parts. Why is that? Apparently dowel pins, or "locating pins" should be used instead. From my understanding, I suppose it is because there are much tighter…
TwoWaySpeedOfLight
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Is there a standard name for a flanged threaded tube?

I have designed a custom part that I need, but it is so simple I'm sure there must be off-the-shelf versions available. However I don't know what it's called to search for it. The image on the left is the custom part I designed, it's basically a…
jhabbott
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Boeing 737NG pickle fork cracking. What determines the fastener layout?

Boeing 737NG aircraft are currently being checked for cracking in the "pickle fork" assembly that attaches the fuselage to the wings. The affected joint has 4 fasteners that attach the fork to the wing. It's intended mostly to resist shear loads, as…
emrys57
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4
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When are Nyloc nuts indicated instead of cap nuts?

Are there any applications in which a Nyloc nut is preferred to a proper cap nut? As best I can tell: a Nyloc nut is just a specialized cap nut that will fail under lower torque and temperatures than a metal cap nut.
feetwet
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Rule for bolt thread engagement

When bolting something like a flange or a dead/blind end to a port on a pressure vessel (lets say rated to 2 ATM), is there a good rule of thumb on how much of the threading should be engaged into the tapped hole in the vessel? Is there an ISO…
Beo
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Aerospace bolts and washer combination

In my aerospace company we have repetitive discussions regarding the stacking of low tolerance fasteners with non-countersunk washers. For example a fastner NAS6703-X (size 10) has a max. base radius of .02". A non-countersunk washer NAS1149 size 10…
Vitus
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Cleaning Shavings from Tapped Hole

I have a hole that contains metal shavings after I have tapped it. Is there a common method to clean out metal shavings from between the threads of the tapped hole?
Zero
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Hot Dip Galvanized Nuts

I’m in a position where I need to order high volumes of nuts and bolts for a project. I read through a South African National Standard, SANS 2001-CS1, in which it states that when I use hot dip galvanized fasteners the nut should be of a higher…
Noble
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