Which Bolt Do You Need? Pole-Line Bolts & Fasteners Explained
Pole-line bolts are chosen by what they fasten. A machine bolt is the general-purpose bolt for fixing crossarms and hardware through a pole or member. A double-arming bolt is threaded at both ends to fix crossarms on both sides of a pole (double-arming) and take guy/hardware attachments. An eye bolt provides an attachment eye for a fitting, guy, or conductor hardware. A U-bolt clamps a round or square member to a structure. Match the bolt to its job, confirm the size/grade for the load, and specify the correct finish.
Bolts and fasteners are the small parts that hold the whole line together, and there’s a specific bolt for each job. Using the wrong one means a poor or unsafe fixing. This guide walks through the main pole-line bolts and how to choose.
The Main Pole-Line Bolts
Machine bolt: the general-purpose fixing
A square-head machine bolt is the workhorse a threaded bolt (often square-headed for grip) used to fix crossarms, brackets, and hardware through a pole or member, secured with a nut and washer. When you need to bolt a fitting to the structure, the machine bolt is usually the answer. Sized by diameter and length to the members it joins.
Double-arming bolt crossarms both sides
A double-arming bolt is threaded at both ends and runs right through the pole, so it can fix crossarms on both sides (double-arming) and also take guy attachments or additional hardware at its ends. Use it for double-arm construction and where a through-bolt must carry hardware on both faces of the pole.
Eye bolt an attachment eye
A forged eye bolt provides a load-rated eye through a structure an attachment point for a guy, an insulator string, or conductor hardware. Where you need a fixed eye to hang or anchor something, the eye bolt provides it. Related fittings include the eye nut (an eye on a nut, for a bolt or rod end) and the thimble eye bolt (an eye bolt with an integral thimble for a strand).
U-bolt clamp a member
A U-bolt is a U-shaped bolt that clamps a round or square member (a pole, a pipe, a bar) to a structure or bracket, secured with nuts. Use it to attach or clamp a member rather than to bolt through one.
Other Common Pole-Line Fasteners
- Hex bolt and nut – standard hex fasteners for general assembly.
- Clevis bolt – provides a clevis (jaw) attachment on a structure.
- Cable extension bolt – extends an anchor rod to the surface for deep-set anchors.
- Upset bolt and pigtail bolt – special-head bolts for particular fixings.
- Square washer – distributes the bolt load on timber or steel so the nut/head doesn’t pull through.
How Do I Choose the Right Bolt?
1. Start with the job
- Fixing a crossarm/bracket through a member → machine bolt.
- Crossarms on both sides of the pole / through-bolt with end hardware → double-arming bolt.
- Need an attachment eye → eye bolt (or eye nut / thimble eye bolt).
- Clamp a round/square member to a structure → U-bolt.
- Extend an anchor rod → cable extension bolt.
2. Size it to the members and the load
The bolt’s diameter and length are set by the members it joins and the load it carries. It must be long enough to pass through and take the nut/washer, and strong enough for the load with your safety margin. Grade and load ratings are datasheet figures to confirm for structural fixings.
3. Don’t forget the washer
A square washer (or the correct washer) spreads the load so the nut or head doesn’t crush or pull through the member especially important on timber. Specify washers with the bolts.
4. Specify the finish
Outdoor line hardware should be hot-dip galvanized for corrosion life (see our finish guide). Confirm the finish for the environment the bolt should age with the hardware it holds.
5. Match the standard
Bolt dimensions and grades follow standards (ISO, ASTM, DIN). Match the bolt to your specification’s standard so it meets the required grade and fit. (See our guide on bolt standards for the ISO/ASTM/DIN detail.)
A Note on the Fasteners Category
Pole-line bolts, nuts, washers, and banding form a fastener family that runs across every structure on the line crossarms, guys, anchors, brackets. Buying them as a coordinated set (right bolt, right washer, right finish, matched to the members) avoids the field problem of a fixing that’s the wrong length, grade, or finish. Specify the fasteners with the hardware they hold.
Which Bolt Do You Need? FAQ
What is a machine bolt used for? A machine bolt is the general-purpose pole-line bolt for fixing crossarms, brackets, and hardware through a pole or member, secured with a nut and washer. It’s the default bolt when you need to fasten a fitting to the structure. Size it by diameter and length to the members.
What is a double-arming bolt? A double-arming bolt is threaded at both ends and runs through the pole, letting you fix crossarms on both sides (double-arming) and take guy or hardware attachments at its ends. Use it for double-arm construction and through-bolt fixings that carry hardware on both faces.
When do I use an eye bolt vs an eye nut? An eye bolt provides an attachment eye through a structure (bolted through a member). An eye nut provides an eye on a nut, threaded onto a bolt or rod end. Use an eye bolt to create an eye through the structure; use an eye nut to add an eye to a bolt/rod end.
What is a U-bolt used for? A U-bolt clamps a round or square member a pole, pipe, or bar to a structure or bracket, secured with nuts. Use it to attach or clamp a member, rather than to bolt through one.
Why do I need a washer with pole-line bolts? A washer (often a square washer) spreads the bolt load so the nut or head doesn’t crush or pull through the member especially on timber. It protects the member and keeps the fixing tight. Specify the correct washers with the bolts.
What finish should pole-line bolts have? Hot-dip galvanized, for outdoor corrosion life, so the bolt ages with the hardware it holds. Confirm the finish and the grade/standard (ISO/ASTM/DIN) for your specification and environment.
The Bottom Line
Choose a pole-line bolt by its job: machine bolt for general crossarm/hardware fixing, double-arming bolt for crossarms both sides and through-bolt hardware, eye bolt for an attachment eye, U-bolt to clamp a member plus hex bolts, clevis bolts, washers, and specials for particular fixings. Size to the members and load, add the right washer, specify a galvanized finish, and match the standard.
DAPENG Power (DP Power Fitting) manufactures the full pole-line fastener range machine bolts, double-arming bolts, eye bolts, eye nuts, U-bolts, hex bolts and nuts, clevis bolts, square washers, and more, all part of the pole line hardware range. Tell us the members, the load, and your standard, and we’ll specify the right bolts and fasteners.
