Full Thread Transmission Tower Bolts: Specification & Sourcing Guide

A full thread transmission tower bolt is a hex head structural fastener that is threaded along its entire shank, so the nut can be positioned anywhere within the bolt length instead of only at a fixed thread run-out. In tower, substation and communication steel work, that is the reason full thread bolts are requested for variable plate packs, adjustable bracing and splice connections. YM Structural Bolts is the transmission and structural fastener line of Ningbo Yuema Fastener Co., Ltd., a fastener manufacturer established in 2012 in Ningbo, Zhejiang, China, producing full thread and semi-threaded tower bolts from M12 to M64 in property classes 4.8, 8.8, 10.9 and 12.9.

This guide is written for the research-to-evaluation stage of procurement: engineers and buyers who already know they need a fully threaded bolt but still have to lock down thread coverage, coating, grade, certification scope, documentation and delivery. It walks through the constraints that actually define a purchasable item, then shows how a full thread order is specified, validated and documented.

Why 'Full Thread' Alone Is Not a Purchasable Specification

A purchase order that says only 'full thread transmission tower bolt' leaves four variables open, and each of them changes price, fit and the certificate package that can be issued against the order.

• Thread coverage against grip length. A fully threaded shank removes the unthreaded section, so the nut position becomes adjustable along the bolt length. The buyer still has to state bolt length, plate pack thickness and where the nut is expected to sit. Whether the thread run is acceptable inside a given shear plane is a joint design decision that should be confirmed by the project engineer, not assumed from the bolt description.
• Coating build-up on the thread. Hot dip galvanized (HDG) coating is applied to the finished bolt, and the coating sits on the thread as well as the shank. A fully threaded bolt therefore has more coated thread surface than a semi-threaded bolt of the same length, so bolt-to-nut fit has to be confirmed on the assembled set rather than on the bolt alone.
• Standard and property class. ASTM A394 covers steel transmission tower bolts in Type 0 (HDG low/medium carbon), Type 1 (HDG medium carbon, quenched and tempered) and Type 3 (bare weathering steel); Type 2 has been withdrawn. The property class and the governing standard must be named together, because a class 8.8 or 10.9 bolt and an ASTM A394 Type 1 bolt are not interchangeable statements on a drawing.
• Documentation. A tower bolt order is only as good as its paperwork: material test certificate (MTC), batch traceability, mechanical test and salt spray test records. These are separate line items in the specification and should be requested before quotation, not after shipment.

Where Full Thread Bolts Sit in the Transmission Tower Market

Demand for tower bolts follows tower construction, and tower construction is still dominated by lattice structures. Coherent Market Insights places lattice towers at a 72.3% share of the transmission tower market in 2026, and these structures connect steel members with structural bolts. Spherical Insights estimates the global power transmission lines and towers market at USD 39.10 billion in 2026, with transmission towers as the fastest-growing segment. The same source places Asia Pacific at 63% of global power transmission infrastructure market share in 2025.

Bolt volume per structure is high enough that specification details become a procurement issue rather than a detail. Published procurement estimates for a typical 132 kV transmission tower put the requirement at 1,200 to 2,500 bolts depending on tower type: suspension towers around 1,200–1,500, angle towers around 1,800–2,200 and dead-end towers around 2,000–2,500. At that scale, the choice between full thread and semi-threaded bolts affects how many bolt lengths a project has to stock, because a fully threaded bolt can serve several plate pack thicknesses with one length.

The trade-off is that flexibility has to be paid for in specification discipline. A fully threaded bolt used where a fixed thread run-out was intended moves the nut position and changes the effective clamping arrangement, so tower designers and buyers generally fix the thread form per connection type rather than per project.

Full Thread Transmission Tower Bolts from YM Structural Bolts

YM Structural Bolts supplies full thread and semi-threaded hex head tower bolts, heavy hex structural bolts and wind tower bolts, together with the matching nuts and washers, from a 20,000 m² facility in Ningbo, Zhejiang. The product family is manufactured to ASTM A325(M) and ASTM A490(M), and to DIN 912, DIN 931, DIN 933, DIN 975, DIN 7990, DIN 6914, DIN 6915, DIN 6916, ISO 4014, ISO 4016, EN 14399, AS 1252, BS 3692, BS 4190, BS 4395, JIS B1180 and JIS B1181. ASTM A394, A325 and A490 certification can be supplied with a material test certificate.

Dimensional and mechanical envelope

For a fully threaded M24 power tower hex bolt, the practical outcome of this envelope is that diameter, length, pitch, class and coating are all selectable independently — which is what allows one bolt length to cover several connection details on the same tower family.

Nut, washer and assembly fit

A fully threaded bolt is only useful if the nut travels the full length of the thread. YM Structural Bolts supplies heavy hex nuts for transmission towers to DIN 934, ISO 4032 and ASTM A194 2H, in carbon steel, alloy steel or stainless steel (SS304 available), with property classes 5, 6, 8, 10 and 12, metric M series threads and a 6H thread tolerance. The matching heavy flat washer conforms to ASTM F436 and DIN 125A / DIN 125B, with strict dimensional tolerances for matching with the bolts and nuts, and can be supplied with inspection records and MTC.

The 6H nut tolerance is the reference point buyers should quote when they ask for a coated bolt-and-nut assembly: the assembly, not the bolt alone, is what has to run freely along the full thread and then hold torque on site.

Coating options for a fully threaded shank

Finish options are hot dip galvanized, zinc plated, black oxide and Dacromet. Hot dip galvanized and Dacromet coatings provide anti-corrosion protection for outdoor tower projects, and both are routinely specified for power transmission towers; zinc plated and black oxide are the lighter-duty options. Because a full thread bolt exposes coated thread over its whole length, the coating decision should be made together with the nut fit check and the site environment, not after the bolts are produced.

Where the tower is remote and unattended, an anti-theft variant is available: the bolt uses a breakaway head design, so the driving head separates once the specified torque is reached and standard spanners have no gripping surface left to unscrew the fastener. This is supplied as an anti-theft bolt with nut in assembly form.

Certification and documentation package

For European-style structural bolting assemblies, YM Structural Bolts holds a Certificate of Conformity of Factory Production Control issued by LRQA Nederland B.V. under EN 15048-1:2007, certificate number 0343/CPR/SHA/BIG00002843/B, covering non-preloaded structural bolting assemblies, issued 19 June 2025 and valid to 18 June 2028. A separate EN 14399 schedule, certificate number 0343/CPR/SHA/BJG00002843/A, covers EN 14399-3 and EN 14399-4 bolts in M12–M36 diameter and 35–200 mm length in property classes 8.8 and 10.9 (HR finish) and 10.9 (HV finish), the matching nuts in classes 8 and 10, and EN 14399-5 and EN 14399-6 washers in D12–D36.

Management system certificates are held under ISO 9001:2015 (certificate 37825Q15701R2S, Euroswiss Certification Co., Ltd., valid 5 August 2025 to 22 September 2028), ISO 14001:2015 (37825E22789R0S, valid 5 August 2025 to 4 August 2028) and ISO 45001:2018 (37825S12401R0S, valid 5 August 2025 to 4 August 2028). Batch traceability is maintained, and mechanical and salt spray tests are performed before delivery.

How to Specify and Validate a Full Thread Tower Bolt Order

The sequence below turns a general requirement into an order that can be quoted, produced and inspected without renegotiation. Each step produces a document or a decision that the next step depends on.

1. Classify the joint and the grip range. Split the tower bill of materials by connection type (leg splice, bracing, dead-end, substation steel) and record the plate pack thickness range for each. This is the step that decides full thread versus semi-threaded, and it is the step buyers most often skip.
2. Fix diameter, length and pitch. Select from M12 to M64 and 20 mm to 2000 mm, with thread pitch between 1.5 mm and 3.0 mm. Non-standard pitch is available on request, so a custom non-standard transmission tower bolt does not require a new tooling programme.
3. Set the property class and match the nut. Choose 4.8, 8.8, 10.9 or 12.9 for the bolt and a compatible nut class from 5, 6, 8, 10 or 12 with 6H thread tolerance. Naming the assembly prevents a bolt that meets its class from being paired with a nut that does not.
4. Choose the coating against the site environment. Hot dip galvanized or Dacromet for outdoor tower and substation exposure; zinc plated or black oxide where the service condition allows. Confirm the bolt-and-nut fit after coating on the full thread length.
5. Name the governing standard and the certificate package. State ASTM A394, A325 or A490, or the relevant DIN, ISO, EN, AS, BS or JIS standard, and state whether an MTC, third-party inspection or a CPR certificate reference is required.
6. Approve the assembly and the test plan. Approve bolt, nut and washer as one set. YM Structural Bolts runs tensile test, hardness test, salt spray test and dimension inspection in its in-house lab on every batch before shipment, with 100% pre-shipment testing and third-party inspection available.
7. Confirm commercial terms and delivery. Production runs on OEM/ODM terms with customization to customer requirements, a MOQ of 500 kg and a lead time of 30–45 days. Shipment is from the Ningbo factory via Ningbo port.

Use Cases: Where Full Thread Tower Bolts Are Specified

• High voltage transmission towers and communication towers. Steel-to-steel connections where plate packs vary and the nut position must be adjustable on site.
• Substation steel structures. Busbar support frames, gantries and equipment structures that use tower bolt assemblies in galvanized finish.
• Foundation and anchor connections. Bent anchor bolts and J-type anchor bolts for transmission towers use a threaded portion that allows setting tolerance; the same full thread logic applies to the exposed length.
• Wind tower and photovoltaic mounting structures. Both appear in the same fastener family and the same galvanized finish requirement as power towers.
• Rail transit supports, steel structures and heavy machinery connections where class 8.8 or 10.9 bolts with HDG coating are specified.
• Remote and unattended towers where the anti-theft breakaway head variant is specified to prevent disassembly after installation.

Field experience in the Gulf market is documented for this product family: 1,200,000 sets have been supplied for high voltage transmission and communication tower construction in the United Arab Emirates, and 50,000,000 sets to Saudi Arabia over a 25-year supply relationship, with a reported anti-theft rate of 100%, a bolt loosening rate below 0.3% and zero structural safety incidents. The product design service life is stated as 35 years under normal outdoor environment.

Comparison Table: Full Thread vs Semi-Threaded Tower Bolts

Neither form is better in general. Full thread buys adjustment range and SKU consolidation; semi-threaded buys a defined bearing section. The correct choice is per connection, and it should be written on the drawing rather than left to the supplier.

FAQ: Full Thread Transmission Tower Bolts

Next Step: From Specification to a Quoted Full Thread Bolt Set

The shortest route through this specification is to send three documents together: the connection list with plate pack thicknesses, the required standard and property class, and the coating and documentation requirements. With those three inputs, a full thread tower bolt order can be quoted as a complete assembly — bolt, heavy hex nut and washer — rather than as separate parts that have to be matched later.

YM Structural Bolts supplies full thread and semi-threaded transmission tower bolts from M12 to M64 in classes 4.8 to 12.9, in hot dip galvanized, Dacromet, zinc plated or black oxide finish, with MTC, batch traceability and mechanical and salt spray test records, from Ningbo Yuema Fastener Co., Ltd. in Ningbo, Zhejiang, China.