The primary function of the nut in any threaded assembly is to act as the instrument through which the tension is induced into the bolt or screw and to continue to retain that tension and thus, the clamp load in the assembly.
The vast majority of nuts have hexagon drive faces but they come with a large variety of other features for a secondary purpose such as thread locking, face seating/location, load spreading, pinning, welding, capping.
All the machine screw threads, ISO-METRIC - coarse and fine, UNC, UNF BSW, BSF, BA, are available.
Materials include carbon steels, stainless steels, brass, aluminium, nylon.
Finishes would normally include plain, zinc, galvanised, chrome.
Correct strength combinations of nuts and bolts will ensure that the nut is capable of tensioning the mating bolt to breaking point rather than the nut stripping; (a broken bolt is clearly evident, a stripped nut may not be). To ensure correct combinations, always use bolt and nut products with the same proof load designations.
eg: SAE Grade 8 bolts use Grade 8 nuts.
SAE Grade 5 bolts use Grade 5 nuts.
Property Class 8.8 bolts use Class 8 nuts.
Note: Property Class 4.6 bolts use Class 5 nuts.
Products purchased as a bolt and nut combination will be supplied with the correct nut by the manufacturer.
Nut Styles
PLAIN HEXAGON The standard form general purpose nut Ð may be used with various washers.
Also available in a thin or lock nut version. (JAM)
Normally supplied double chamfered if cold formed.
May also come with full bearing or washer face when machined.
HEXAGON SLOTTED A plain hexagon nut with slots cut to allow insertion of a split cotter pin through the nut and a drilled hole in the bolt totally preventing subsequent rotation in either direction.
Often used in a non-tensioned assembly.
HEXAGON CASTLE Deeper than slotted so that full thread engagement is not compromised by the slots.
In addition, the cotter pin head and split ends will be less proud when spread.
Usually machined and with a washer face.
(Whiz Lock)
Special serrations on the flange face resist loosening in vibration applications.
Also available as a plain flange to span a large hole or slot or spread the clamp load.
A nylon insert on top of the nut creates a prevailing torque, resists loosening and allows reuse after several removals without significant performance loss.
Also available in thin series.
Manufactured with a cone shaped top which is distorted after tapping to create a prevailing torque.
Less reusable than nylon insert, but less susceptible to high temperature applications.
Incorporates a stainless spring steel insert developing prevailing torque to resist loosening.
Also reusable without significant loss of performance.
Less susceptible to high temperature or caustic applications.
After tapping, a plain hexagon nut is distorted on three of the hexagon faces creating an internal thread distortion designed to create a prevailing torque.
Low level reusability.
(Clinch) NUT
Nut has a central spigot and a conical machined undercut around the spigot.
This nut is inserted into a thin sheet panel and the spigot peened over to secure it.
Can also come with nylon insert.
HEXAGON WELD NUT Has three welding projections designed to melt and weld to a panel when special equipment applies high electrical current and high pressure.
Can have a central spigot to aid location and prevent weld spatter entering threads.
SQUARE WELD NUT Has four welding projections.
Works as above, but does require flatter surface.
Can come with or without central spigot designed for location and to prevent weld splatter from fouling the thread.
Either machined with a closed domed end or capped in a secondary process after tapping.
Used in decorative applications, or for protection from protruding threads. Usually chromed or polished.
HEXAGON WHEEL NUT Formed with a cone or taper end designed to mate with the tapered recess in an automotive wheel, giving positive location and increased bearing surface.
(Thick) NUT
Similar to the deep nut above except longer/deeper.
Used for connecting lengths of all thread.
Similar to the deep nut above except longer/deeper.
Used for connecting lengths of all thread.
Tee Nuts A pressed metal threaded product with spiked prongs.
Designed to embed in timber to provide a solid thread form mostly found in furniture applications.
Thin Locknuts (Jam Nuts)
When used in conjunction with a standard nut with the intention of 'locking' the assembly, these nuts are commonly assembled incorrectly.
The correct assembly method is to apply the thin nut FIRST as shown in the diagram below.
Tension the thin nut to snug tight - Force 1.
Apply the standard nut and tension it to snug tight - Force 2
While holding the thin nut against rotating, further tighten the standard nut to full design tension - Force 3 and Force 4
In effect, the two nuts are now working in opposite directions and are locked. The upper nut has to carry the higher load and therefore, has to be the thicker of the two.
These nuts will remain locked even if tension in the assembly is lost.
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