Locknuts

What is a locking nut / lock nut?

A lock nut or locking nut serves, for example, to secure a cable gland and prevents the screw nuts from loosening. For example, a cable gland can be furnished with a WISKA lock nut so that the screw nuts are not loosened by vibrations. With its hexagonal shape, a lock nut generally resembles the actual nut, but is usually flatter. Aside from polyamide, they are made of nickel-plated brass or stainless steel.

How do I tighten a locking nut?

Tightening a locking nut requires a sensitive touch. If too much torque is exercised on the locking nut, which is generally very flat, this may lead to damage to the thread or to a tensile fracture of the screw. Therefore, it is necessary to ensure that the lock nut is not overtightened. As the lock nut has a thread running in the opposite direction, it must not be overtightened to prevent the connector from loosening.

What applications and materials are there for locking nuts?

The ATEX lock nut is used in areas with a high risk of explosion, for example on a cable gland. These include, for example, the Ex lock nut, which effectively counteracts sparks and withstands an explosion pressure.

An EMC locking nut, e.g. from Lapp, is characterised by integrated cutting edges, which allow safe contact with coated housings. In comparison with a twist nipple, which only seals inserted cables, cable glands, which are additionally secured with a locking nut made of brass or corrosion-resistant stainless steel, also serve to provide strain relief for a cable.

Thread sizes of locking nuts in inches and metric millimetres

A locking nut in accordance with DIN 439 has an internal fine thread. A locking nut in accordance with DIN is generally referred to as a lock nut with metric external dimensions, as are predominantly used in Europe. However, the locking nut with a size in inches is also widespread, e.g. in the automotive industry. The locking nut with a PG (Panzerrohrgewinde) connector is also common as a third alternative. We have summarised the most common sizes for locknuts in the table below.

Millimetre	Metric	Inch (NPT)	PG
6 mm	Locknut M6	-	-
8 mm	Locknut M8	-	-
10 mm	Locknut M10	-	-
12 mm	Locknut M12	Locknut 1/2 Inch	PG7
16 mm	Locknut M16	Locknut 3/4 Inch	PG9
20 mm	Locknut M20	Locknut 1 Inch	PG11
25 mm	Locknut M25	Locknut 1 1/2 Inch	PG16
32 mm	Locknut M32	Locknut 2 Inch	PG21
40 mm	Locknut M40	-	PG36
50 mm	Locknut M50	-	PG42
63 mm	Locknut M63	-	PG48
75 mm	Locknut M75	-	-

What types of locknuts are available?

Our range includes among others:

Plastic locknut / counter nut from Lapp, optionally with metric or PG internal thread. Made of high-strength polyamide. Suitable for a temperature range of 80 or 100 degrees, depending on the version.
Brass locking nut / lock nut, with a nickel-plated surface, e.g. with an external diameter of 95, 114 or 135 mm. Designed for a temperature range from -60 to 200°C.
Stainless steel locking nuts / lock nuts, corrosion-resistant and available in standard sizes, for example M12, M16, M20, M25 and M50. Available in thicknesses 1.5 mm, 2.8 mm or 5 mm, among others
ATEX / EX locking nuts / lock nuts, suitable for applications in potentially explosive environments, for example for cable glands on control cabinets and electrical equipment. Made of nickel-plated brass and available with metric or PG internal threads in various sizes.

Overview of the metric threads in cable glands

Nominal size, metric	Clamping range (approx. data)	External diameter of the thread in mm	Pitch
M12 cable gland	3 - 7 mm	12.0	1.5
M16 cable gland	4.5 - 10 mm	16.0	1.5
M20 cable gland	7 - 13 mm	20.0	1.5
M25 cable gland	9 - 17 mm	25.0	1.5
M32 cable gland	11 - 21 mm	32.0	1.5
M40 cable gland	19 - 28 mm	40.0	1.5
M50 cable gland	27 - 35 mm	50.0	1.5
M63 cable gland	34 - 45 mm	63.0	1.5

M threads in accordance with EN 60423 or IEC 423 or BS 6053 ISO 68/DIN13

But regardless of whether it is a WISKA cable gland or a Lapp cable gland e.g. a SKINDICHT or SKINTOP cable gland: The mode of operation is similar for all manufacturers. a connector has a seal as well as a union nut and a locking nut.