Description
The Fitting That Starts the Insulator String at the Structure
An insulator string has to begin somewhere, at the crossarm, the tower attachment, or the yoke, and it has to begin with a coupling that can take whatever the structure offers on one side and hand off to the first insulator on the other.
That fitting is the ball eye: an eye at one end, which bolts or pins to the structure hardware, and a ball at the other, which drops into the socket of the first insulator and is retained by a clip. It is the top link of the chain, and, like the top link of any chain, it carries everything hanging below it.
This page publishes the coupling sizes and rated loads, ties the ball designation to your insulator, and settles the question buyers ask most often at this point in a drawing: ball eye, ball clevis, socket eye, or socket clevis, which one goes here?
Ball Eye, Ball Clevis, Socket Eye, Socket Clevis – Which Fitting?
Four fittings, one logic. Each has a coupling end (ball or socket) and an attachment end (eye or clevis):
| Fitting | Coupling end | Attachment end | Use at the structure end when |
|---|---|---|---|
| Ball eye (this page) | Ball – enters the insulator socket | Closed eye | The structure attachment is eye/pin type |
| Ball clevis | Ball – enters the insulator socket | Clevis jaw + pin | The structure attachment is tongue type |
| Socket eye | Socket – receives the insulator ball | Closed eye | (Used at the conductor end of the string) |
| Socket clevis | Socket – receives the insulator ball | Clevis jaw + pin | (Used at the conductor end of the string) |
The rule: at the structure end of a suspension string you need a ball fitting (ball eye or ball clevis), because the first insulator presents a socket to receive it. Choose eye vs clevis by what the structure offers, an eye/pin attachment takes the eye; a tongue attachment takes the clevis. At the conductor end, the mirror applies: a socket fitting receives the last insulator’s ball. Read the ball/socket from the insulator and the eye/clevis from the hardware, and the fitting is decided.
Ball Eye Selection Table
(Hot dip galvanized. Designated coupling size and rated failing load are catalog-verified; intermediate dimensions pending PDF verification – see note above.)
| Designated coupling size (mm) | Rated failing load (kN) | Weight (kg) |
|---|---|---|
| 16 | 70 | 0.3 |
| 16 | 70 | 0.3 |
| 16 | 100 | 0.3 |
| 16 | 120 | 0.4 |
| 20 | 120 | 0.5 |
| 20 | 160 | 0.5 |
| 20 | 160 | 0.5 |
| 20 | 210 | 0.7 |
| 20 | 210 | 0.9 |
| 24 | 200 | 1.0 |
| 24 | 300 | 1.1 |
| 24 | 320 | 1.2 |
| 28 | 420 | 1.5 |
(Full dimensional columns – d, φ, b, d1, h – to be published once verified against the original catalog PDF. Sizes and configurations outside this range are forged to your drawings.)
Reading the table: note that a single coupling size (16 mm, 20 mm, 24 mm) spans several rated loads. Coupling size and rated load are two separate specifications. The coupling size must match your insulator’s ball designation; the rated load must match your string’s design class. Specify both, or you may receive a fitting that couples correctly but caps the string’s strength.
How to Select a Ball Eye in Three Checks
1. Coupling designation, from the insulator, exactly: The ball must match the socket on your insulator. Ball-and-socket couplings are standardized, IEC 60120 defines the common designations, with 16 mm and 20 mm the most frequently specified. A 16 mm ball will not seat in a 20 mm socket; read the designation off the insulator datasheet and quote it.
2. Rated failing load, match the string, never undercut it: The string is rated at its weakest component, and the ball eye sits at the top carrying all of it. Our fittings run in matched classes so a coherent string is easy to build:
- Ball eye – 70 to 420 kN (table above)
- Socket eye / socket clevis – 70 to 300 kN
- U shackles – 70 to 170 kN
- Yoke plates – 100 to 600 kN
Quote the string’s design rating once and everything returns in the same class.
3. Eye dimension against the structure hardware: The eye must fit the pin, bolt, or shackle it connects to. An eye correctly rated but dimensioned for a smaller pin is a fitting that goes back in the box – check it against the U shackle or attachment it meets.
Why Buyers Choose DAPENG Ball Eyes
- Forged in one piece: Hot-forged carbon steel, no welds in the load path, the whole string’s load passes through the ball neck and the eye, so the strength must be in the grain.
- Ball machined to the coupling standard: The ball seats fully in the insulator socket, articulates freely, and presents a clean clip channel, so the retaining clip seats properly and the coupling holds.
- Galvanizing you can measure: Hot-dip galvanized to ISO 1461 / ASTM A153 class coatings, checkable with a gauge at goods-in, the ball neck included, where a thin coat and high stress meet.
- Rated loads that are tested: RFL marked per fitting, batch load-tested, reports supplied, your string’s safety factor rests on a tested figure.
- The whole string from one factory: Ball eyes ship with the ball clevises, socket eyes, socket clevises, U shackles, yoke plates, insulators and terminal clamps of the same assembly, matched in class, kitted per structure.
Use-Case Deep Dive
Where does a ball eye sit in a suspension string?
At the top. A standard suspension assembly runs: structure attachment → U shackle → ball eye → insulator string → socket clevis or socket eye → suspension clamp → conductor. The eye connects to the shackle or attachment above; the ball enters the socket of the first insulator below. On tension assemblies the same ball eye starts the string, with a strain clamp or bolt type tension clamp terminating the conductor at the far end; on twin-string arrangements a yoke plate distributes to two ball eyes.
What does the retaining clip do, and why check it?
The ball eye’s ball is held in the insulator socket by a retaining clip, the same clip system covered on our socket eye page. It is the only component preventing the ball from lifting out of the socket, it is fitted by hand at height, and its omission or mis-seating is a leading string-assembly error. Push the ball fully home, seat the clip so it cannot back out, and check every one visually, and never substitute wire or a nail for a proper clip. We supply clips with the fittings so nothing is improvised on the tower.
Can I match ball eyes into a string from another supplier?
Yes, with two checks in writing: the coupling designation (ball size) and the rated load class of the neighboring fittings, sent as figures, samples, or clear photographs with a rule in frame. We confirm mating and class before production. Mixed-supplier strings are normal on networks built over decades; the risk is the unchecked assumption that everything shares a coupling size and a rating.
Specifications and What They Mean for You
| Specification | What we supply | What it means for the buyer |
|---|---|---|
| Body | Hot-forged carbon steel, one piece | No weld in the load path at the string’s top link |
| Coating | Hot-dip galvanized, ISO 1461 / ASTM A153 class | Decades outdoors; thickness checkable, ball neck included |
| Coupling sizes | 16, 20, 24, 28 designated; custom to drawing | Matches your insulator’s socket designation exactly |
| Rated failing loads | 70 to 420 kN | Match or exceed every other fitting in the string |
| Retention | Clips supplied with fittings | The coupling arrives complete; nothing improvised at height |
| Verification | Batch load testing, reports with shipment | Safety factors calculated from tested numbers |
Straight Answers to Common Buyer Concerns
“How do we verify a forged coupling is rated as marked?” Test evidence before it ships and a gauge check when it lands: batch load-test reports with every order, galvanizing thickness measurable at goods-in, and third-party pre-shipment inspection (SGS/BV or your nominated agency) welcome at the factory. On the top link of a string, we would rather your inspector confirmed the rating at our gate than your outage report questioned it later.
“Our utility standard specifies a coupling we don’t see in the table.” Then we forge to it. Utilities specify ball designation, eye dimensions, marking and sometimes proof-load documentation, manufacturing to a customer’s drawing is the bulk of our export work. Send the specification page or a sample; confirmation drawings are issued before production.
“Can we order maintenance quantities?” Coupling fittings usually ship within complete string assemblies, but spares orders are welcome, tell us the quantity and we quote honestly, freight arithmetic included.
Complete the String
- Ball clevises – the clevis-attachment alternative at the structure end
- Socket eyes and socket clevises – the coupling fittings at the conductor end
- U shackles (70–170 kN) – the structure attachment above the ball eye
- Yoke plates (100–600 kN) – where one attachment feeds multiple strings
- Insulators – the ball-and-socket units this fitting couples
- Suspension clamps, strain clamps, bolt type tension clamps – terminal hardware
- Browse all overhead line fittings and pole line hardware
Get a String-Matched Quote Within 24 Hours
Send your insulator datasheet, string drawing and design rating, or a photograph of the fitting you’re replacing with a rule in frame. Our engineers confirm the coupling designation, load class, and eye dimensions, flag any mismatch in the chain, and return a factory-direct quotation, typically within one working day.
After You Order
Confirmation drawings before production, batch load-test reports and galvanizing certificates with shipment, retaining clips packed with the fittings, and assemblies kitted per string so stores issue complete sets rather than loose parts, with engineering support that stays reachable through stringing and beyond.
