Screw Set Screws
Screw Set Screws
Lift and Turn tub stopper with no set screw?
I have a lift and turn tub stopper. According to Lowe's you need to loosen the set screw to get these out. I have looked at mine and there is no set screw. I am pretty sure that it is not a roller ball or pop-up drain, but again, no set screw. The dang thing will not come out!! Any ideas for me? Thanks.
Screw
From Wikipedia, the free encyclopedia
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This article is about the threaded fastener. For other uses, see Screw (disambiguation).
Screws come in a variety of shapes and sizes for different purposes. U.S. Quarter coin (diameter 24 mm) shown for scale.A screw is a shaft with a helical groove or thread formed on its surface and provision at one end to turn the screw. Its main uses are as a threaded fastener used to hold objects together, and as a simple machine used to translate torque into linear force. It can also be defined as an inclined plane wrapped around a shaft.
Contents [hide]
1 The screw as simple machine
2 Threaded fastener
3 Differentiation between bolt and screw
3.1 Other fastening methods
4 Materials and strength
5 Mechanical analysis
6 Tensile strength
7 Types of screws and bolts
8 Shapes of screw head
9 Types of screw drive
9.1 Combination drives
10 Tamper-resistant screws
11 Tools used
12 Mechanics of use
13 Thread standards
13.1 ISO metric screw thread
13.2 Whitworth
13.3 British Association screw threads (BA)
13.4 Unified Thread Standard
13.5 Others
14 History
15 Legal issues
16 See also
17 References
18 External links
[edit] The screw as simple machine
Archimedes (287 BC – c. 212 BC) invented the Archimedes' screw. The device is a large screw in a pipe used in antiquity and to the present day to pump liquids.
A screw may be used to move one object, with a threaded hole right through it, relative to another object to which one end of the screw is fastened allowing it to rotate but not to move axially. A vise tool is an example of this use. In effect, a wood screw also acts this way.
Because it moves forward in a screwing motion, the propeller of a ship is called a screw. Likewise, the of an aircraft is called an airscrew.
[edit] Threaded fastener
The remainder of this article is mainly concerned with the screw as threaded fastener.
A screw used as a threaded fastener consists of a shaft, usually mainly cylindrical and in many cases tapering to a point at one end and with a helical ridge or thread formed on it, and a head at one end which can be rotated by some means. The thread is essentially an inclined plane wrapped around the shaft. The thread mates with a complementary helix in the material. The material may be manufactured with the mating helix using a tap, or the screw may create it when first driven in (a self-tapping screw). The head is specially shaped to allow a screwdriver or wrench (British English: spanner) to rotate the screw, driving it in or releasing it. The head is of larger diameter than the body of the screw and has no thread so that the screw can not be driven deeper than the length of the shaft, and providing compression.
Screws can normally be removed and reinserted without reducing their effectiveness. They have greater holding power than nails and permit disassembly and reuse.
The vast majority of screws are tightened by clockwise rotation; we speak of a right-hand thread. Screws with left-hand threads are used in exceptional cases, when the screw is subject to anticlockwise forces that might undo a right-hand thread. Left-hand screws are used on rotating items such as the left-hand grinding wheel on a bench grinder or the left hand pedal on a bicycle (both looking towards the equipment).
Threaded fasteners were made by a cutting action such as dies provide, but recent advances in tooling allow them to be made by rolling an unthreaded rod (the blank) between two specially machined dies which squeeze the blank into the shape of the required fastener, including the thread. This method has the advantages of work hardening the thread and saving material. A rolled thread can be distinguished from a thread formed by a die as the outside diameter of the thread is greater than the diameter of the unthreaded portion of the shaft. Bicycle spokes, which are just bolts with long thin unthreaded portions, always use rolled threads for strength.
[edit] Differentiation between bolt and screw
See also: Bolt manufacturing process
A bolt passes through a hole of larger diameter than its thread, and is held in place by a nut or similar device; it is not designed to be turned. What is often referred to as a bolt is in fact a cap screw, which is designed to be turned (or screwed). Cap screws may, or may not be used with nuts. The distinction is subtle, but significant in the design of the fastener. If threaded all the way to the back of the head a cap screw becomes a machine screw.
[edit] Other fastening methods
Alternative fasteners to screws and bolts are nails, rivets, roll pins, pinned shafts, welding, soldering, brazing, gluing, and duct tape (taping).
Another option is the threaded insert. Examples include HeliCoil [1] and Keensert [2].
[edit] Materials and strength
Screws and bolts are made in a wide range of materials, with steel being perhaps the most common, in many varieties. Where great resistance to weather or corrosion is required, stainless steel, titanium, brass or bronze may be used, or a coating such as brass, zinc or chromium applied. Electrolytic action from dissimilar metals can be prevented with aluminium screws for double-glazing tracks, for example. Some types of plastic, such as nylon or Teflon, can be threaded and used for fastening requiring moderate strength and great resistance to corrosion or for the purpose of electrical insulation. Even porcelain and glass can have molded screw threads that are used successfully in applications such as electrical line insulators and canning jars.
The same type of screw or bolt can be made in many different grades of material. For critical high-tensile-strength applications, low-grade bolts may fail, resulting in damage or injury. On SAE-standard bolts, a distinctive pattern of marking is impressed on the heads to allow inspection and validation of the strength of the bolt. However, low-cost counterfeit fasteners may be found with actual strength far less than indicated by the markings. Such inferior fasteners are a danger to life and property when used in aircraft, automobiles, heavy trucks, and similar critical applications.
[edit] Mechanical analysis
Rotating screw and fixed troughA screw or bolt is a specialized application of the inclined plane. The inclined plane, called its thread, is helically disposed around a cylinder or shaft. That thread usually either fits into a corresponding (negative or "female") helical thread in a nut, or forms a corresponding helical cut in surrounding softer material as it is inserted. A simple screw, e.g. for fastening, is typically pointed, and thereby is commonly distinguished (in informal terminology) from a bolt or "machine screw." Common screws, and usually bolts, have a "head" which may be mechanically driven or rotated, which usually serves as a stop, and may have an unthreaded "shoulder" portion beneath the head. A wide variety of other secondary features exists.
The technical analysis (see also statics, dynamics) to determine the pitch, thread profile, coefficient of friction (static and dynamic), and holding power of a screw or bolt is very similar to that performed to predict wedge behavior. Wedges are discussed in the article on simple machines.
Critical applications of screws and bolts will specify a torque that must be applied when driving it. The main concept is to tension the bolt, and compress parts being held together, creating a spring-like assembly. The stress thus introduced to the bolt is called a preload. When external forces try to separate the parts, the bolt experiences no strain unless the preload force is exceeded.
As long as the preload is never exceeded, the bolt or nut will never come loose (assuming the full strength of the bolt is used. If the full strength of the bolt is not used (e.g., a steel bolt threaded into aluminum, then a thread-locking adhesive or insert may be used.
If the preload is exceeded during normal use, the joint will eventually fail. The preload is calculated as a percentage of the bolt's yield tensile strength, or the strength of the threads it goes into, or the compressive strength of the clamped layers (plates, washers, gaskets), whichever is least.
[edit] Tensile strength
Rusty hexagonal bolt headsScrews and bolts are usually in tension when properly fitted. In most applications they are not designed to bear large shear forces. For example, when two overlapping metal bars joined by a bolt are likely to be pulled apart longitudinally, the bolt must be tight enough so that the friction between the two bars can overcome the longitudinal force. If the bars slip, then the bolt may be sheared in half, or friction between the bolt and slipping bars may erode and weaken the bolt (called fretting). For this type of application, high-strength steel bolts are used and should be tightened to a specified torque.
High-strength steel bolts usually have a hexagonal head with an ISO strength rating (called property class) stamped on the head. The property classes most often used are 5.8, 8.8, and 10.9. The number before the point is the tensile ultimate strength in MPa divided by 100. The number after the point is 10 times the ratio of tensile yield strength to tensile ultimate strength. For example, a property class 5.8 bolt has a nominal (minimum) tensile ultimate strength of 500 MPa, and a tensile yield strength of 0.8 times tensile ultimate strength or 0.8(500) = 400 MPa.
Tensile ultimate strength is the stress at which the bolt fails (breaks in half). Tensile yield strength is the stress at which the bolt will receive a permanent set (an elongation from which it will not recover when the force is removed) of 0.2 % offset strain. When elongating a fastener prior to reaching the yield point, the fastener is said to be operating in the elastic region; whereas elongation beyond the yield point is referred to as operating in the plastic region, since the fastener has suffered permanent plastic deformation.
Mild steel bolts have property class 4.6. High-strength steel bolts have property class 8.8 or above. An M10, property class 8.8 bolt can very safely hold a static tensile load of about 15 kN.
There is no method to measure the tension of a bolt already in place other than to tighten it and identify at which point the bolt starts moving. This is known as 're-torqueing'. An electronic torque wrench is used on the bolt under test, and the torque applied is constantly measured. When the bolt starts moving (tightening) the torque briefly drops sharply - this drop-off point is considered the measure of tension.
[edit] Types of screws and bolts
Combination flanged-hex/Phillips-head screw used in computersA hex cap screw has a protruding hexagonal head, designed to be driven by a spanner or wrench.
A socket cap screw has a hexagonal recessed drive, usually with a cylindrical head, but can also be found with a rounded button head or a countersunk flat head.
Wood and chipboard screws have a tapered shaft. A hole of about the diameter of the shaft, but less than the diameter of the thread, is often drilled into the wood; screws can be driven into undrilled wood, but there is a risk of splitting the workpiece. Chipboard is less likely to split. A hole can be drilled in brick, concrete, or other hard materials, and a wall plug inserted; a woodscrew can then be driven into the plug.
Lag screw, lag bolt or coach screw refers to a large wood screw with a head, square or hexagonal, driven by a wrench rather than a screwdriver.
A Machine screw has a cylindrical shaft, threaded its entire length, and fits into a nut or a tapped hole.
Self-tapping screws or thread cutting screws have sharp threads that cut into a material such as sheet metal or plastic. They are sometimes notched at the tip to aid in chip removal during thread cutting.
A Self-drilling screw is similar to a self-tapping screw, but has a drill-shaped point to cut through the material without prior drilling.
Thread rolling screws have a lobed (usually triangular) cross section. They form threads by pushing outward during installation. They may have tapping threads or machine threads.
A Drywall screw is a specialized self-tapping screw designed to bind drywall to wood or metal studs, but it has proven to be a versatile construction fastener.
A Set screw, used to prevent loosening due to vibration, is available with thumb screw, square head, Hex head (inset socket) and, most commonly, headless (a grub screw in UK parlance, designed to be inserted flush with or below the surface of the work piece). Alternatively defined to be a screw whose thread reaches the head (if any), as opposed to a bolt.
Dowel screw is a wood screw with two pointed ends and no head, used for making hidden joints between two pieces of wood.
A wood screw being driven into a board with a drillA stud is similar to a bolt but without the head. Studs are threaded on both ends. In some cases the entire length of the stud is threaded, while in other cases there will be an unthreaded section in the middle. It may be anchored in concrete, for example, with only the threads on one end exposed. (See also: screw anchor, wedge anchor.)
An Eye bolt used for attaching cables to a surface.
A carriage bolt or coach bolt has a domed or countersunk head, and the shaft is topped by a short square section under the head. The square section grips into the part being fixed (typically wood), preventing the bolt from turning when the nut is tightened. A rib neck carriage bolt has several longitudinal ribs instead of the square section, to grip into a metal part being fixed.
A stove bolt is similar to a carriage bolt, but usually used in metal. It requires a square hole in the metal being bolted to prevent the bolt from turning.
The Superbolt, or Multi-Jackbolt Tensioner is an alternative type of fastener that retrofits or replaces existing nuts, bolts, or studs. Tension in the bolt is developed by torquing individual jackbolts which are threaded through the body of the nut and push against a hardened washer. Installation and removal of any size tensioner is achieved with hand tools, which can be advantageous when dealing with large diameter bolting applications.
Acme screw form has threads that are stronger and broader than standard V-profile threads, making them much better for load carrying, linear actuating (also see ball screws), and quick threading. It is often used for vise screws.
A Shoulder Screw is a screw used for revolute joints in mechanisms and linkages. The main shank of the screw is smooth and works as a suitable bearing surface. At the end of the cylindrical bearing surface is a reduced diameter thread.
[edit] Shapes of screw head
(a) pan, (b) button, (c) round, (d) truss, (e) flat, (f) oval
pan head: a low disc with chamfered outer edge.
button or dome head: cylindrical with a rounded top.
round head: dome-shaped, commonly used for machine screws.
truss head: lower-profile dome designed to prevent tampering.
flat head or countersunk: conical, with flat outer
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