Nuts

Hexagon Full Nuts

Full Nuts are the most regularly used mating nut with a bolt or screw.
Full Nuts are either cold or hot forged depending on the diameter size. They can also be machined from bar.
Designated in the EN ISO 4032 standard as two styles, plain nuts are either Style 1, which is a thin height nut and Style 2 which is a thick height nut, approximately 10% larger than Style 1.
Each style has appropriate features and physical conditions i.e. heat-treated or non- heat- treated for carbon steel nuts.
Standard nuts must be marked to signify the strength grades on sizes above M5 diameter.
For full nuts in other materials, then the style geometry characteristics remain but variations on marking and testing will change. For stainless steel plain nuts refer to EN ISO 3506-2 and non-ferrous BS EN 28839.

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Slotted Nuts are standard nuts in accordance with nut Style 2. The contours and the depth of the slots are very important with regard to the strength characteristics of the nut when in application.
Slotted nuts are available in various property classes, both heat-treated and non-heat treated. The designating of the strength grades is obligatory and must be identified by marking the nut.
The application of slotted nuts is unique to the use of steel pins and taper or split pins, to lock the slotted nut into position after tightening. The pin is inserted through the slot and a hole passing through the fastener to secure a substantial joint.

Castle Nuts are forged and also machined.
The difference between a slotted nut and a castle nut is the latter has turret geometry on the top of the nut. The nut thicknesses are the same as a slotted nut.
Like slotted nuts, castle nut applications are similar using steel pins and taper or split pins, to lock the nut into position after tightening. The pin is inserted through the slot and a hole through the fastener to secure the joint.
Castle nuts are used when the locking pins are required to be flush with the diameter of the turret. This is useful for those applications where confined space is at a minimum and pin protrusion is unacceptable.
Castle nuts are both heat-treated and also non-heat treated. Strength grades must be identified and marked on the nut accordingly.

Lock nuts are available in various materials and finishes; carbon steel, stainless steel, brass etc.
M16 diameter and below have a double chamfer.
Above M20 the top surface has a chamfer, whilst the underside will have a washer bearing surface.
Useful in combination with small diameter rolled thread machine screws.
Not ideal for load bearing bolted joint assemblies but useful when used in combination with plain nuts, noting that the lock nut should be in contact with the mating surface of the joint and the plain nut assembled on top. This assists rigidity when required.

Self-Locking Nuts, also referred to as 'Stiffnuts', are prevailing torque nuts.
Either the internal threads have an engineered interference system to resist loosening, or there is some other device inserted e.g. a Nylon insert into the nut, or deforming the diameter to prevent the nut from loosening under vibration.
There are many proprietary designs, in various materials, and testing is advisable to establish the resistance to vibration and fatigue.
The reference standard for prevailing torque type steel nuts is ISO 2320:1997.
Self-locking nuts only work in one direction, related to the position of the element of interference.

Nyloc Nuts have a nylon insert, whereas Philidas Nuts, Binx Nuts and Aerotight Nuts are classed as Allmetal Self Locking Nuts.