Many different types of lock nuts are available for use in a wide range of applications.Â While their underlying mechanisms might vary, they all have one thing in common: they produce additional resistance to vibrational loosening forces without using lock washers which improves efficiencies in many manufacturing processes.
Lock nuts typically fall into one of two groups:
- PREVAILING TORQUE – an intrinsic feature of the lock nut produces friction between threads of mated components thereby increasing the resistance to loosening forces. The two main categories of prevailing torque type nuts include: all metal and nylon insert lock nuts.
- SURFACE-BEARING – a free spinning nut that requires tightening against a bearing surface in order for the locking mechanism to function. Two common surface bearing type lock nuts include: serrated flange and KEPS (K-Lock)
1-Prevailing Torque Type Lock Nuts:
All metal prevailing torque type lock nuts achieve their prevailing torque by altering the shape of the nut in some way – most commonly by distorting the threads of the nut which then bites into the mating part when tightened. These include: 2-way reversible lock nuts, Flex-Type Lock Nuts, Stover Lock Nuts.
A one piece all metal prevailing torque type hex nut with two or three equally spaced round or rectangular impressions compressed into the flat sides of the nut. These compressions create slight distortion in the internal threading that results in an increased resistance when tightened onto mating threads.Â Two way reversible lock nuts are considered “two way” because they can be installed in either orientation (top up, top down) These nuts are also referred to asÂ center lock nuts, and are ideal for production and automated assembly. As a result the locking of the mating part occurs in the center of the nut. This saves on screw length, because threads need not protrude from the nut to lock securely.Â Since they are all-metal, they are more resistant to higher temperatures and chemical exposure than non-metallic lock nuts (such as nylon insert lock nuts).
Â A one piece all metal prevailing torque type hex lock nut with six equally spaced opposing slots aligned with the corners of the nut that are cut into a cylindrical section of slightly smaller diameter at the top of the nut. It is this slotted section that locks the nut in place by increasing resistance to loosening forces when tightened onto a mated thread.Â These are considered as one-way because they can only be installed one way – top up.Since they are all-metal, they are more resistant to higher temperatures and chemical exposure than non-metallic lock nuts (such as nylon insert lock nuts).
A one piece all metal prevailing torque type hex lock nut with a conical top with chamfered corners. The resistance to loosening forces is created by distortion in the top threads.Â These are considered as one-way because they can only be installed one way – top up. Since they are all-metal, they are more resistant to higher temperatures and chemical exposure than non-metallic lock nuts (such as nylon insert lock nuts).
Nylon insert torque prevailing type lock nuts contain a captive (permanent) undersized nylon (or other polymer) insert that grips the mating threads when tightened and generates the prevailing torque.Â The nylon insert also dampens vibration between the bolt and nut further securing the mated components and provides a gas and moisture seal. Because the threads of the mating bolt deform but do not cut into the nylon so nylon insert lock nuts may be re-used a limited number of times. These nuts are considered one-way lock nuts because they can only be installed one-wayâ€”top up.Â Unlike all-metal nuts, the nylon insert limits the use at elevated temperatures or when exposed to certain chemicals.
2-Surface-Bearing Lock Nuts:
A one piece all-metal lock nut with aÂ flanged bearing surface that increases the surface area substantially and has circular serrations radiating outwards.Â Unlike prevailing torque tyes, this bearing lock nut does not lock onto mating threads. It is a free spinning nut until the serrations contact and displace material on the mating surface upon tightening. Depending on surface finish, localized surface corrosion may occur.Â The serrations are designed not to interfere with the tightening of the nut, but once tightened against a bearing surface, the teeth produce a ratchet-type locking mechanism resistant to vibrational and other loosening forces.Â The serrated flange eliminates any need for a washer or lock washer. The increased flange size relative to the rest of the nut distributes the load over a greater area. Furthermore it is ideal for irregular or over-sized holes.Â Since they are all-metal, they are more resistant to higher temperatures and chemical exposure than non-metallic lock nuts (such as nylon insert lock nuts).
An all-metal hex nut pre-assembled with a free spinning lock washer often external tooth. Unlike prevailing torque types , this bearing lock nut does not lock onto mating threads.Â Rather it is a free spinning nut that must be firmly tightened against a bearing surface so the teeth of the lock washer can bite into the surface onto which it is being tightened.Â It is the washer that resists vibrational loosening forces. Depending on surface finish, localized surface corrosion may occur as the lock washer bites into and removes the surface treatment.Â Since they are all-metal, they are more resistant to higher temperatures and chemical exposure.
Key Considerations When Choosing Specific Styles of Lock Nuts:
- Select the correct lock nut for the specific task at hand
- Good design ensures savings in the long run
- Re-use (need to disassemble/reassemble components)
- Localized corrosion – (Surface finish onto which the nut is tightened)
- Length of thread exposure (top-lock vs center-lock)
- Exposure to chemicals
- Exposure to extreme temperatures
- Size and shape of hole
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Aspen Fasteners stocks full lines of lock nuts in steel. stainless steel and metricÂ in addition to most other screws, nuts, bolts and washers. Available for same day shipping from distribution centers across the USA. And remember, it’s always free shipping. Expedited next day delivery is also available for those rush requirements.
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