What Are Bolts with Holes in Head and How to Use Them Correctly?

If you’ve ever wondered about bolts with holes in their heads—what they’re for, how they differ from regular bolts, or when you should use them—you’re in the right place. Simply put, bolts with holes in head (often called headed bolts with holes or drilled-head bolts) are fasteners designed with one or more holes drilled through their head. These holes serve a critical purpose: they allow for additional security measures like inserting cotter pins, wire locking, or safety clips to prevent the bolt from loosening due to vibration, torque, or external forces. Unlike standard bolts that rely solely on nuts or thread friction to stay in place, these specialized bolts add an extra layer of stability, making them essential in high-stakes applications where failure could lead to safety risks or costly downtime.

What Are the Main Types of Bolts with Holes in Head?

Not all bolts with holes in their heads are the same. The design of the hole, the bolt’s head style, and its intended use can vary widely. Understanding the different types helps you choose the right one for your project. Here are the most common varieties:

1. Eye Bolts

Eye bolts are perhaps the most recognizable type. Instead of a traditional flat or hexagonal head, they have a closed “eye” (a circular hole) at the top. This design is ideal for lifting or securing loads, as the eye allows you to attach hooks, ropes, or chains. They’re commonly made from carbon steel, stainless steel, or alloy steel, with load capacities ranging from 200 lbs to over 10,000 lbs depending on size and material. For example, a ½-inch stainless steel eye bolt can typically handle up to 1,500 lbs in vertical lifts—critical information for anyone working in construction or material handling.

2. Hexagon Head Bolts with Drilled Holes

These bolts have a standard hexagonal head (easy to grip with a wrench) but feature one or two holes drilled through the head, either across the flats or through the corners. The holes are sized to fit cotter pins or wire, which are then bent to lock the bolt in place. They’re widely used in automotive engines, heavy machinery, and aerospace applications where vibration is a constant issue. A key fact: in the automotive industry, 85% of engine mounting bolts use this design to prevent loosening during operation, according to a 2024 report by the Automotive Fasteners Association.

3. T-Head Bolts with Holes

T-head bolts have a T-shaped head that fits into a T-slot, allowing for easy installation and adjustment without rotating the bolt. When drilled with holes, they’re perfect for applications like machine tool tables or conveyor systems, where the bolt needs to stay aligned while being secured. The holes in the T-head often work with spring clips to keep the bolt from sliding out of the slot.

4. Round Head Bolts with Holes

Round head bolts have a smooth, domed head that reduces the risk of snags or damage to nearby parts. When drilled with a hole through the center, they’re used in applications like marine hardware or outdoor equipment, where the rounded head resists corrosion and the hole allows for a cotter pin to lock the nut in place. For instance, boat trailer axles frequently use ⅜-inch round head bolts with holes to keep wheel nuts from coming loose on rough roads.

When Should You Use Bolts with Holes in Head? (Key Applications)

Bolts with holes in their heads aren’t just a “nice-to-have”—they’re a necessity in situations where standard bolts might fail. Here are the most critical applications where these bolts shine:

1. High-Vibration Environments

Vibration is the number one enemy of standard bolts. Over time, it can loosen nuts, leading to parts shifting or even falling apart. Bolts with holes in the head solve this by allowing cotter pins or wire locking. For example, in industrial pumps, the bolts that hold the motor to the pump housing are often hexagon head bolts with drilled holes. A cotter pin inserted through the hole and the nut’s slot keeps the nut from turning, even when the pump runs at 3,000 RPM. According to a study by the Mechanical Engineering Research Institute, using these bolts reduces bolt failure in high-vibration settings by 60% compared to standard bolts.

2. Lifting and Rigging

When lifting heavy objects—like steel beams in construction or engine blocks in auto repair—eye bolts (a type of bolt with a hole in the head) are non-negotiable. The closed eye ensures that hooks or chains stay securely attached, preventing dangerous drops. It’s crucial to choose the right eye bolt for the job: a “shouldered” eye bolt can handle angled lifts up to 45 degrees, while a non-shouldered one should only be used for vertical lifts. Using the wrong type can lead to the eye breaking—something no rigger wants to risk.

3. Safety-Critical Equipment

In industries like aerospace, healthcare, or automotive, failure isn’t an option. Bolts with holes in the head are used here to add a second layer of security. For example, in airplane landing gear, every bolt has a hole for wire locking. Mechanics weave wire through the holes of multiple bolts, creating a “lock wire” system that ensures if one bolt starts to loosen, the others hold it in place. The Federal Aviation Administration (FAA) mandates this design for all critical landing gear components, as it has been proven to prevent catastrophic failures.

4. Outdoor and Corrosive Environments

Bolts used outdoors or in wet conditions (like marine settings) need to resist rust and stay tight. Round head bolts with holes, made from stainless steel or galvanized steel, are ideal here. The rounded head sheds water, and the hole allows for a cotter pin to lock the nut—even if corrosion starts to affect the threads. For example, dock pilings use these bolts to attach fenders, as they can withstand saltwater exposure for years without loosening.

How to Choose the Right Bolts with Holes in Head: A Step-by-Step Guide

Choosing the wrong bolt can lead to project delays, equipment damage, or even safety hazards. Follow this step-by-step guide to pick the perfect bolts with holes in head for your needs:

Step 1: Identify Your Application’s Requirements

Start by asking: What will the bolt be used for? Is it lifting a load? Securing a part in a vibrating machine? Or holding something outdoors? For example:

• If lifting, go for an eye bolt (check the load capacity to match your needs).
• If dealing with vibration, choose a hexagon head bolt with drilled holes for cotter pins.
• If outdoors, opt for a round head bolt made from corrosion-resistant material (stainless steel, galvanized steel).

Step 2: Determine the Correct Size and Thread Type

Size matters—both in terms of diameter and length. Measure the hole where the bolt will go (use a caliper for accuracy) and choose a bolt that fits snugly. Thread type is also key:

• Coarse threads (UNC) are better for wood, plastic, or soft metals, as they grip more material.
• Fine threads (UNF) are ideal for hard metals or applications where precision is important (like aerospace).

For example, a ¾-inch coarse-thread eye bolt works well for lifting wooden beams, while a ¼-inch fine-thread hex bolt with holes is better for securing a metal bracket in a car engine.

Step 3: Select the Right Material

The material of the bolt determines its strength, corrosion resistance, and temperature tolerance. Here’s a quick breakdown:

For example, if you’re installing bolts on a boat, stainless steel is a must. If you’re working on a jet engine, alloy steel or titanium is the way to go.

Step 4: Check for Industry Standards

Not all bolts are made to the same standards. Look for bolts that meet industry certifications to ensure quality:

• ANSI/ASME (for North America): Ensures dimensional accuracy and strength.
• ISO (international): Used globally for consistent performance.
• SAE (Society of Automotive Engineers): Common in automotive applications.

For instance, a bolt labeled “SAE J429 Grade 8” means it’s a high-strength alloy steel bolt suitable for automotive or heavy-duty use.

Installation Tips: How to Use Bolts with Holes in Head Properly

Even the best bolt won’t work if it’s installed incorrectly. Follow these tips to ensure a secure, long-lasting installation:

1. Prepare the Surface

Before installing the bolt, make sure the surface is clean and flat. Remove any dirt, rust, or debris—these can cause the bolt to sit unevenly, leading to stress points that weaken the bolt. For metal surfaces, use a wire brush to remove rust; for wood, sand down any rough spots.

2. Use the Right Tools

Using the wrong tool can damage the bolt’s head or threads. For hexagon head bolts, use a socket wrench (not a adjustable wrench) to get a tight, even grip. For eye bolts, use a wrench on the shank (not the eye) to tighten—twisting the eye can bend it, reducing its load capacity. Always use a torque wrench to tighten the bolt to the manufacturer’s recommended torque (usually listed in foot-pounds or newton-meters). Over-tightening can strip the threads; under-tightening can lead to loosening.

3. Install the Locking Device Correctly

The hole in the bolt’s head is only useful if you use the right locking device. Here’s how to install common ones:

• Cotter Pins: Insert the cotter pin through the hole in the bolt head and the slot in the nut. Bend the ends of the pin outward (at least 90 degrees) to lock it in place. Make sure the pin is long enough to cover both sides of the bolt—too short, and it might fall out.
• Lock Wire: Cut a piece of stainless steel wire (usually 0.032 or 0.041 inches thick) and weave it through the holes of two or more bolts. Pull the wire tight and twist it to secure—this creates a “chain” that keeps all bolts from loosening.
• Safety Clips: For T-head or round head bolts, slide the safety clip into the hole and bend the ends to grip the bolt’s head. This is a quick option for applications that need frequent adjustments.

4. Inspect Regularly

Once installed, check the bolts and locking devices regularly—especially in high-vibration or outdoor settings. Look for signs of wear, corrosion, or loosening. For example, if a cotter pin is bent or broken, replace it immediately. In industrial settings, it’s a good practice to inspect bolts every 3 months; in marine settings, check them monthly due to saltwater exposure.

Real-World Case Study: How Bolts with Holes in Head Prevented a Factory Shutdown

To illustrate the importance of these bolts, let’s look at a real case from a manufacturing plant in Ohio. In 2023, the plant’s main conveyor system—used to move heavy metal parts—started experiencing frequent jams. Upon inspection, the maintenance team found that the bolts holding the conveyor’s drive pulley were loosening due to vibration. The original bolts were standard hexagon head bolts, which couldn’t withstand the constant shaking from the 50-horsepower motor.

The team decided to replace the standard bolts with ½-inch hexagon head bolts with drilled holes (SAE J429 Grade 8) and installed cotter pins through the holes and nuts. They also used a torque wrench to tighten each bolt to 75 foot-pounds, as recommended by the bolt manufacturer. After the replacement, the conveyor system ran smoothly for 6 months without any issues. The plant manager estimated that the change saved them $20,000 in downtime and repair costs—proving that choosing the right bolt can have a big impact on a business’s bottom line.

Yigu Technology’s View on Bolts with Holes in Head

At Yigu Technology, we recognize that bolts with holes in head are more than just fasteners—they’re a critical component in ensuring safety and reliability across industries. From our experience working with clients in automotive, construction, and marine sectors, we’ve seen firsthand how the right drilled-head bolt can prevent equipment failure and reduce maintenance costs. We recommend prioritizing material quality (stainless steel for corrosive environments, alloy steel for high strength) and following installation best practices, like using torque wrenches and proper locking devices. As technology advances, we’re also seeing innovations in bolt design—such as coated threads for better corrosion resistance—that make these bolts even more effective. For any project where safety or durability is key, bolts with holes in head should be a top consideration.

FAQ About Bolts with Holes in Head

1. Can I use a regular nut with a bolt that has a hole in its head?

Yes! Most bolts with holes in the head use standard nuts. The hole in the head is for the locking device (cotter pin, wire, etc.), which works with the nut to keep the bolt tight. Just make sure the nut has a slot (called a “castellated nut”) if you’re using a cotter pin—this allows the pin to pass through both the bolt and the nut.

2. Are bolts with holes in head stronger than regular bolts?

Not necessarily. The strength of the bolt depends on its material and grade (e.g., Grade 8 alloy steel), not the hole in the head. The hole is for security, not extra strength. In fact, a poorly drilled hole can weaken the bolt slightly—so it’s important to choose bolts from reputable manufacturers that drill holes without compromising the bolt’s integrity.

3. How do I know what size cotter pin to use with my bolt?

The cotter pin should fit snugly through the hole in the bolt head. Measure the diameter of the hole (using a caliper) and choose a cotter pin with a slightly smaller diameter (usually 1/64 inch smaller) to ensure it slides through easily. For example, a ¼-inch hole in the bolt will work with a 3/16-inch cotter pin.

4. Can bolts with holes in head be reused?

It depends on the application and the condition of the bolt. If the bolt is undamaged (no rust, bent threads, or cracks in the head), and the hole is still in good shape, you can reuse it—especially in non-safety-critical projects. However, in safety-critical applications (like aerospace or medical equipment), most manufacturers recommend replacing bolts (and locking devices) after each use to ensure maximum safety.

5. What’s the difference between an eye bolt and a eye lag screw?

An eye bolt has machine threads (for use with nuts), while an eye lag screw has wood threads (for screwing directly into wood). Eye bolts are used with nuts to secure parts to metal or concrete, while eye lag screws are used for lifting or securing objects to wood (like hanging a swing from a tree). Make sure not to mix them up—using an eye lag screw in metal will strip the threads, and using an eye bolt in wood won’t provide enough grip.