Tower Bolt

What is a tower bolt?

Hobson's tower bolt is a hot dip galvanised hex bolt in low temperature carbon steel to AS 1559, supplied with a single nut and washer, for transmission towers and electrical distribution: the bolts that join the angle members of steel lattice towers. Hobson says they are suitable for low temperature applications, and the bolts are marked with HEC, TL, M and the nominal bolt length.

In hardware stores "tower bolt" can also mean a sliding bolt for doors and gates. These are not that: they are galvanised structural bolts for tower steelwork.

Hobson publishes no property class, proof load, tensile strength, temperature limit or tightening torque for these bolts in the documents we hold. The bolt size, length, number and tightening in a tower come from the tower designer or asset owner's specification.

Tower bolt sizes, thread and plain shank

Every tower bolt we carry. The thread length is the same for every length of a size, so a longer bolt has a longer plain (unthreaded) shank. Hobson's bolts and set screws article gives the plain shank as the bolt length minus the thread length, and notes the shank has a larger shear area than the threaded section. Which length a joint needs, and where the thread may sit, comes from the tower drawings. Select a row to open that bolt in the selector.

Spanner size and markings

• •M16 tower bolts are 24mm across flats and M20 tower bolts 30mm, on Hobson's Did You Know sheets. The sheets do not cover M12.
• •Head marking: HEC (Hobson's manufacturing mark), TL, M and the nominal bolt length.
• •Each bolt comes with one nut and one washer. Extra flat tower washers to AS 1559 (hot dip galvanised to AS/NZS 1214, 5mm thick, thicker than standard flat washers, M12 to M24) are on the structural washer page.

Hot dip galvanised for exposed steelwork

Hobson rates hot dip galvanising as high corrosion resistance and recommends it for long term outdoor use, and its corrosion guide for metal connectors gives hot dip galvanising or stainless as the minimum for steel exposed to the weather, with stainless only in the sea spray zone. The guide is written for building connectors; for towers the asset owner's specification sets the coating. Our tower bolts come hot dip galvanised only.

Hobson's article on galvanising explains that today's galvanised bolts are a duller matt grey than older ones: the brightness has no effect on performance, and coating mass sets the life.

Ordering and using tower bolts

1. Take the size and length from the tower drawings or the asset owner's bolt schedule.
2. Check the grip: the plain shank in the table tells you how much of each length is unthreaded.
3. Order extra flat tower washers if the drawings call for more than the one supplied.
4. Tighten to the tower specification. Hobson publishes no torque for these bolts.
5. Hobson's sheets say test certificates can be downloaded from its website if your project needs them.

Tower bolts in Adelaide

Allmat supplies tower bolts, flat tower washers, nuts and bolting tools to line crews, electrical contractors and steel fabricators across Adelaide and South Australia. Send us your bolt schedule and we will price the lot.

Questions