Hex Flange Nut

What a flange nut is and why use one

A hex flange nut is a hex nut with a wide washer face (the flange) made in one piece with it. The flange spreads the clamp load like a washer, so no separate washer is needed, and Hobson notes that makes flange nuts ideal for difficult to reach areas where loose nuts and washers are hard to handle.

Hobson lists its serrated flange nuts for machinery and equipment such as forklifts, trucks, harvesters, conveyors, tractors and excavators, and tags some sizes for pallet racking, sheds, HVAC and solar panel mounting.

Serrated, plain, cone lock or nylon flange nut?

• •Serrated flange nut: ridges on the bearing face embed into the joint material as the nut is tightened. Hobson's technical paper on vibration loosening explains that this raises the friction under the nut, so it takes more torque to break it loose. The serrations need the joint to stay tensioned to work, they add no prevailing torque, and they mark the surface, so consider whether the surface can take that.
• •Plain flange nut (no serrations): the same built-in washer face with a smooth bearing face, to DIN 6923 (class 8) or ISO 4161 (class 10, M24 to M36). The choice where the surface should not be marked by serrations.
• •Cone lock flange nut (DIN 6927, class 10): Hobson says the cone lock adds prevailing torque to the connection to protect against loosening, and the flange body removes the need for a washer.
• •D-Lok serrated flange nut (class 12, zinc flake): made to pair with D-Lok class 12.9 serrated flange bolts, which Hobson designed for applications with constant vibration such as equipment and machinery, conveyors, trucks, mining equipment, forklifts and motorbikes.
• •Nylon flange nut: natural nylon, which Hobson lists for protecting surfaces, good electrical insulation and absorbing shocks and vibration.
• •Cable tray nut: Hobson recommends it with its cable tray bolt for installing splice plates, brackets or other accessories into cable trays or ladders.

Metric flange nut ranges

One row per range we carry. Select a range to open it in the selector, then pick the size. All are coarse thread except the two fine pitch rows.

Imperial UNC and UNF flange nuts

Serrated flange nuts to IFI 145. Hobson lists the UNF grade 8 nuts for the automotive industry and machinery, and notes they are commonly used on exhaust manifolds. UNC and UNF are different threads: match the nut to the bolt.

Flange nut spanner sizes

Spanner sizes (across flats) from Hobson's sheets. They differ between ranges at some sizes, so check the range you buy.

Matching the flange nut to the bolt

1. Thread: the size and the pitch. Metric coarse is the everyday thread; fine pitch, UNC and UNF are different threads and do not mix.
2. Strength: match the nut class to the bolt. Hobson's nyloc torque sheets pair class 8 nuts with class 8.8 bolts and class 10 with 10.9, and its D-Lok sheet pairs the class 12 nut with the class 12.9 D-Lok bolt. For imperial, the general practice is grade 5 nuts on grade 5 bolts and grade 8 on grade 8.
3. Finish: the same finish as the bolt, so one part does not corrode first.

Flange nut finishes and materials

From Hobson's finish comparison, its Bumax data sheet and its nylon data:

• •Zinc plated: 5 microns with a clear passivate, for indoor and non-corrosive conditions.
• •Zinc yellow passivate: 5 microns, more corrosion resistant than zinc plated, for low corrosion conditions or temporary fixing.
• •Hot dip galvanised: 50 microns, high corrosion resistance, recommended for long term outdoor work. Hobson notes no evidence of zinc whiskers has ever been found on its hot dip galvanised range, which it suggests for sensitive places such as data centres.
• •Zinc flake silver (D-Lok): a 10 micron coating with high corrosion resistance and no risk of hydrogen embrittlement.
• •Plain: no coating, supplied lightly oiled.
• •304 and 316 stainless: 316 has molybdenum added for better resistance near the sea. Neither is made to sit in seawater, and salt spray left to build up can mark even 316. Stainless threads can gall (lock up): Hobson suggests a slower installation speed and lubricating the threads with a molybdenum disulphide based lubricant.
• •Bumax 88: high strength stainless; Hobson's Bumax data sheet says Bumax 88 has strength properties that correspond to 8.8 carbon steel fasteners.
• •Nylon: PA6.6 (nylon 66). Hobson's nylon properties sheet gives PA6.6 a working temperature of -30 to +100°C; that is a figure for the material, not a rating of the nut. Nylon absorbs moisture from the air, which makes it less stiff.

Flange nuts in Adelaide

Allmat supplies flange nuts, bolts and washers to mechanics, fabricators, electricians and trade across Adelaide and South Australia. Add the nuts to a quote with the bolts they go on, and we will price the lot.

Questions