Structural Washer

Which structural washer do you need?

• •K0 structural washers (AS/NZS 1252:2016): hardened 35 to 41 HRC, hot dip galvanised or plain. Hobson's K0 range (bolt assemblies, nuts, washers and taper washers) complies with AS/NZS 1252, so these are the washers for K0 structural bolting and for the hardened washer that sits against a DTI. Hobson's Squirter troubleshooting article asks for that washer to be hardened and tempered to at least 320 HV (35 HRC).
• •Flat tower washers (AS 1559): mild steel, hot dip galvanised to AS/NZS 1214 and thicker than standard flat washers (5mm on every size we carry). Hobson's sheet lists them for tower bolt assemblies.
• •H9 Impact washers: hardened (43 to 49 HRC) flat round washers for inch bolts, plain or zinc yellow. Hobson's washer guide gives the hardness; the documents we hold give no other data for them.
• •Schnorr HDS load washers (DIN 6796): conical spring washers in spring steel. Schnorr says they were developed for high strength bolts of grades 8.8 to 10.9, with a spring load matched to 70 to 90% of the bolt load when flattened, to make up for settling in the joint and reduce the dynamic loading on the bolt.
• •Schnorr HS high stress load washers: a load washer with a smaller outside diameter than DIN 6796 and a slightly curved form. Schnorr says they reach the same load as DIN 6796 washers and are used where there is not enough room for them.
• •Nylon washers, including HUBO nylon locking and sealing washers, are on the flat washers page.
• •Not on this page: AS 1252 (1983) structural washers, 8 degree taper washers and EN 14399 K2 washers are on the taper washer page, and DTIs have their own page. TC bolts come with their own washer.

K0 structural and tower washer sizes

Every K0 and tower washer we carry. Select a row to open it in the selector, then pick the finish.

H9 Impact and load washer sizes

Every size we carry. H9 Impact sizes are the bolt size in inches. Select a row to open it in the selector, then pick the finish.

Fitting K0 washers in structural bolting

• •With a DTI: Hobson's DTI documents put the DTI bumps out against a hardened structural washer, never against the turning nut or bolt head. The recommended layout is the DTI under the nut with the hardened washer between the DTI and the nut; a DTI under the bolt head needs an additional hardened washer under the head (see DTI washers). Use the K0 washer (35 to 41 HRC) against a DTI: the AS 1252 (1983) washer on the taper washer page is listed at 26 to 45 HRC, which can fall below the 35 HRC Hobson asks for.
• •Why the hardness matters: Hobson's troubleshooting article says that if the washer is too soft the DTI bumps dig into it, the gap looks closed and there is no squirt, a false sign of tension.
• •Oversize and slotted holes: the same article says an additional round or square washer must be used over a large or slotted hole to give the correct hole size, and the bolt length must be reviewed to allow for it. It gives the hole as no more than 2mm over the bolt diameter for M12 to M24 and 3mm over above M24, as per AS 4100.
• •Sloping flanges take an 8 degree taper washer, not a flat one (see taper washers).
• •TC bolts: use only the washer packed with the bolt. Hobson's TC bolt article says nuts and washers other than the ones dedicated to the bolt shall not be used.
• •The engineer's design and your project specification set the bolt assembly, the washers and the tensioning method.

How Schnorr load washers keep a joint tight

From Schnorr's DIN 6796 table. A load washer is a disc spring: when the bolt is tightened it is pressed flat, and its spring keeps the clamp on if the joint settles. Only the load that remains after the washer has first set protects the joint, so Schnorr gives a minimum height after initial loading, which limits the height lost to setting. Schnorr also lists them as suitable for captive fitting on a wide range of bolts (combi bolts).

Schnorr makes both types to the technical requirements of DIN 267 Part 26. Hobson lists railways among the applications for many of the plain and zinc plated sizes. For the full Schnorr range of safety washers and disc springs, see safety washers and disc spring washers.

Finishes: which one where

• •Hot dip galvanised (K0 and tower washers): Hobson's finish guide rates it high corrosion resistance and recommends it for long term outdoor use, so it is the one for exposed steelwork. Near the coast or in industrial areas, follow the coating your engineer specifies for the bolting.
• •Plain (K0, H9 Impact and Schnorr): no zinc or galvanised coating. Hobson supplies plain products lightly oiled to inhibit rust in the packaging; Schnorr lists its plain load washers as blank and oiled or phosphated and oiled. Use them where the project specification calls for plain, or indoors and dry.
• •Zinc plated and zinc yellow: Hobson rates its zinc plating and zinc yellow low corrosion resistance, for indoor and low-corrosion use. Schnorr's zinc on the HDS and HS load washers is mechanically plated (Zn12M) rather than electroplated.
• •Zinc flake silver and Geomet: zinc flake coatings. Hobson rates zinc flake silver high corrosion resistance without the risk of hydrogen embrittlement. Geomet is a chromium-free zinc and aluminium flake coating that Hobson says meets ISO 10683.
• •Weathering steel: Hobson's AS 4100 article says hot dip galvanised fasteners are not recommended with weathering steel, because contact between the uncoated steel and the zinc causes galvanic corrosion. So do not use the galvanised K0 or tower washers there: Hobson recommends its ASTM F436M weathering steel flat Sampson washers (M24, M30 and M36, on the flat washer page) with its weathering steel bolting.

Structural washers in Adelaide

Allmat supplies K0 structural washers, tower washers, hardened and load washers, with the structural bolts, nuts, taper washers and DTIs that go with them, to steel fabricators, erectors and maintenance crews across Adelaide and South Australia. Send your bolting list and we will price the lot.

Questions