To specify a suspension clevis eye fitting, you need five things: the rated mechanical failing load (kN), the coupling size that matches your insulator, the pin and eye dimensions, the base material, and the galvanizing standard. This guide explains each parameter, shows how they connect to your insulator string, and lists what to put in an RFQ so the quote comes back correct the first time.
Need a datasheet with full dimension drawings? Request the clevis eye specification sheet and our engineers will reply with drawings for your load class.
What Is a Suspension Clevis Eye Fitting?
A suspension clevis eye fitting is a forged steel connector with a clevis (a U-shaped fork closed by a pin) at one end and a round eye at the other. It links a suspension insulator string to the tower cross-arm, or links string components to each other, and carries the full mechanical load of the conductor span.
Because it sits in the load path, its failure means a dropped conductor. This is why buyers specify it by guaranteed strength, not by appearance.
Typical positions in a suspension string:
- Tower side: the clevis eye connects to the cross-arm bracket or a hanger plate.
- Between components: an eye or clevis joins to a ball eye, socket clevis, or yoke plate.
- Line side: it leads toward the suspension clamp or a corona/grading ring bracket.
For the wider category of tower hardware (clamps, shackles, yoke plates, extension links), see our overview of high voltage transmission tower hardware fittings.
How Do You Choose the Rated Load (kN)?
Choose a fitting whose rated mechanical failing load is equal to or higher than your insulator’s specified mechanical load (SML), and never lower. The fitting must not be the weakest link in the string.
Standard strength classes follow the insulator classes used across IEC-based projects:
| Strength class (kN) | Typical insulator class | Typical coupling size (IEC 60120) |
|---|---|---|
| 70 | U70BL | 16 |
| 100 | U100BL | 16 |
| 120 | U120B | 16 |
| 160 | U160BL | 20 |
| 210 | U210B | 20 |
| 300 | U300B | 24 |
| 420 | U420B | 28 |
Reference values for matching. Always confirm against your insulator drawing and project specification.
Two practical rules:
- Match up, not down. If the string is a 160 kN string, every fitting in it must carry at least 160 kN failing load.
- Apply your utility’s safety factor. Many utilities require the maximum working load to stay at or below 40–50% of the failing load. Check your tender document, since this varies by utility and country.
Which Dimensions Must Be Specified?
Specify the clevis width, pin diameter, eye inner diameter, and overall length. These decide whether the fitting physically connects to your insulator, bracket, or clamp.
Clevis end
- Inside width (between fork arms): must fit the mating tongue or plate thickness with working clearance.
- Pin diameter and pin hole: must match the mating part. Ask for pin and cotter pin to be supplied with the fitting.
- Locking device: a stainless steel split pin (cotter pin) is standard. Confirm type and material in the order.
Eye end
- Eye inner diameter and thickness: must match the bracket, hanger plate, or the next fitting.
- Contact surface radius: a smooth radius reduces stress concentration where the mating part bears.
Overall
- Center-to-center length: affects string length and clearance to the tower.
- Weight: useful for freight quotes and installation planning.
If the fitting connects to a ball-and-socket insulator, the mating end must follow the coupling size (see table above). A 16 mm ball cannot be swapped with a 20 mm socket, so confirm the size before you order.
What Material and Coating Should You Require?
Require forged carbon or alloy steel with hot-dip galvanizing to ISO 1461 or ASTM A153. Forging aligns the metal grain along the load direction, which gives higher strength and impact toughness than cast parts of the same size.
| Item | Typical requirement |
|---|---|
| Manufacturing process | Closed-die forging (not casting, not welded plate for main load path) |
| Base steel | Forged carbon steel or alloy steel, grade agreed in drawing |
| Coating | Hot-dip galvanized, ISO 1461 or ASTM A153 |
| Zinc thickness | ISO 1461, articles thicker than 6 mm: local minimum 70 µm, mean minimum 85 µm |
| Pins / cotter pins | Stainless steel or hot-dip galvanized, as specified |
| Marking | Manufacturer mark, rated load, batch number |
If your line runs in a coastal, industrial, or high-humidity area, ask for a higher zinc thickness than the minimum and inspect the threads and pin holes. Corrosion at pin holes is a common field failure point.
Buyers in other markets often cite national standards instead. If your tender references a Chinese standard (for example DL/T 768 forged fittings) or a utility-specific standard, tell us in the RFQ and we will confirm compliance on the datasheet.
Which Tests Should the Manufacturer Show?
Ask for test reports covering mechanical failing load, dimensional check, and zinc coating thickness. IEC 61284 sets the general requirements and tests for overhead line fittings and is the usual reference in international tenders.
Typical test items:
- Visual and dimensional inspection on every lot
- Proof load test: the fitting is loaded to a set percentage of its rated load and must show no permanent deformation
- Failing load test (type test): the sample is loaded until failure, and the result must meet or exceed the rated load
- Zinc coating check: thickness measured with a magnetic gauge, adhesion checked by test
- Material certificate: chemical and mechanical properties of the steel batch
Ask whether the test report is from your supplier’s own lab or an independent third party. For large orders, request the right to witness testing or to have an inspection agency present. You can read how we control quality from forging to final inspection on our factory audit and quality control page.
What to Include in Your RFQ
A complete RFQ gets a correct quote in one round. Include:
- Fitting type (clevis eye, Y-clevis eye, ball eye, socket clevis, etc.)
- Rated mechanical failing load (kN)
- Mating part: insulator coupling size, bracket thickness, or drawing
- Pin diameter and locking device type
- Material and galvanizing standard
- Quantity and delivery port
- Standard or utility specification the project follows
- Test report and inspection requirements
Get the specification sheet. Send us your load class and mating dimensions, and our engineers will return a datasheet with drawings, materials, and test data. Request datasheet and quote →
Frequently Asked Questions
What is the difference between a clevis eye and a ball eye? A clevis eye has a pin-closed fork at one end and a round eye at the other. A ball eye has a ball-shaped end that seats into an insulator’s socket. Use a ball eye when you connect directly to a ball-and-socket insulator, and a clevis eye when you connect to a plate, bracket, or another fitting with a pin.
What kN rating should I choose for a suspension string? Choose a rating equal to or higher than the insulator’s specified mechanical load. For example, a 160 kN insulator string needs fittings rated 160 kN or above. Also apply your utility’s required safety factor, often 40–50% of failing load as the maximum working load.
Which galvanizing standard applies to clevis eye fittings? Hot-dip galvanizing to ISO 1461 or ASTM A153 is the common international requirement. Under ISO 1461, steel articles thicker than 6 mm need a local minimum of 70 µm and a mean minimum of 85 µm zinc coating.
Are forged fittings better than cast fittings? For load-bearing suspension hardware, yes. Forging gives a denser grain structure and higher toughness, which is why most utility specifications require forged steel for the main load path.
Can I use a fitting with a lower rating than the insulator? No. A fitting with a lower failing load becomes the weakest link and can fail before the insulator does. Every component in the string should meet or exceed the string’s rated load.
What documents should the supplier provide? Ask for the datasheet with dimensions, material certificate, galvanizing report, and a mechanical test report. For tenders, also request the type test report against IEC 61284 or the standard your project cites.