Publish Time: 2025-11-30 Origin: Site
Choosing the right door bolt might seem simple, but selecting the correct dimensions is crucial for ensuring proper fit, functionality, and security. A bolt that is too short won’t provide adequate engagement, while one that is too long might not fit the door frame. The thickness, length, and plate size all play a significant role in how well a bolt performs and how much resistance it can offer against forced entry.
Understanding the standard dimensions for different types of bolts—from a simple barrel bolt for a bathroom to a heavy-duty drop bolt for a garage—is the first step toward making an informed decision. This guide provides a comprehensive overview of typical door bolt dimensions, explaining how they vary by type and application. By the end, you’ll know exactly how to measure for and select the perfect bolt for any door in your home or business, ensuring both security and a professional finish.
This table provides a quick reference for common bolt types and their typical dimensions.
| Bolt Type | Common Lengths | Typical Bolt Diameter | Primary Use |
|---|---|---|---|
| Barrel Bolt | 50mm - 200mm | 6mm - 10mm | Interior doors, sheds, cabinets |
| Straight Bolt | 100mm - 300mm | 8mm - 10mm | Double doors, French doors |
| Heavy-Duty Bolt | 150mm - 300mm+ | 12mm - 16mm+ | Gates, garage doors, industrial |
| Flush Bolt | 150mm - 300mm | 8mm - 10mm | Double doors (inactive leaf) |
| Drop Bolt | 150mm - 450mm+ | 12mm - 19mm | Gates, garage doors (floor locking) |
Door bolts come in numerous designs, each suited for specific applications and door types. Their dimensions are standardized to ensure they fit common door and frame setups while providing reliable security.
Barrel bolts are one of the most common types of surface-mounted bolts, valued for their simplicity and effectiveness. They consist of a cylindrical rod (the barrel) that slides into a receiving catch.
Typical Lengths: Barrel bolts are widely available in standard lengths, including 50mm, 75mm, 100mm, 150mm, and 200mm.
Bolt Diameter: The thickness of the bolt rod typically ranges from 6mm for light-duty bolts to over 10mm for heavier versions. A thicker bolt offers greater resistance to shearing forces.
When to Choose Short vs. Long: Shorter bolts (50mm, 75mm) are ideal for small cabinets, cupboards, or lightweight internal doors where high security is not a priority. Longer bolts (150mm, 200mm) provide a deeper and more secure engagement, making them suitable for sheds, gates, and exterior doors.
Plate and Screw Spacing: The mounting plate width is generally between 25mm and 40mm. The spacing of the screw holes is designed to distribute force evenly, and wider plates offer more stability.
Straight bolts, also known as surface bolts, are similar to barrel bolts but often feature a flat or rectangular bolt rod instead of a round one. They are prized for their clean, modern aesthetic.
Lengths: These bolts are typically longer than barrel bolts, with common lengths ranging from 100mm to 300mm. Their slim profile makes them a popular choice for French doors and windows.
Plate Height & Bolt Thickness: The mounting plate height usually ranges from 35mm to 50mm. The bolt itself is often thinner than a barrel bolt, which is suitable for the lower-force applications they are designed for, such as keeping a secondary door leaf stationary.
Recommended Dimensions: For internal double doors, a 150mm or 200mm straight bolt is sufficient. For external applications, choose a length of at least 250mm to ensure secure locking.
When securing gates, garage doors, or industrial entryways, standard bolts are not enough. Heavy-duty bolts are engineered with larger dimensions to withstand significant force.
Lengths: These robust bolts come in lengths of 150mm, 200mm, 250mm, 300mm, and even longer.
Reinforced Plate Dimensions: The mounting plates are significantly thicker and wider, often exceeding 50mm in width, with larger and more numerous screw holes to anchor them securely to the door.
Bolt Rod Diameter: The key feature of a heavy-duty bolt is its thickness. The rod diameter is often 12mm, 16mm, or more, providing superior resistance to cutting or bending. These dimensions are necessary for securing large, heavy doors that are prime targets for forced entry.
Necked bolts, or offset bolts, are designed for situations where the door and frame are not flush. The “neck” is an offset section that allows the bolt to engage a catch on a recessed frame.
Standard Lengths: Necked bolts are commonly found in lengths from 75mm to 150mm.
Offset Measurements: The offset, or “crank,” is the critical dimension. It typically ranges from 15mm to 25mm, allowing the bolt to bridge the gap between the door face and the frame. The angle of the neck is standardized to ensure it aligns correctly with the catch plate.
When Neck Length Matters: Choosing the right offset is essential. Measure the distance between the door surface and the frame surface where the catch will be mounted to select a bolt with the appropriate neck dimension.
Often used on gates and shed doors, sliding bolts have a simple handle that moves the bolt into a locked or unlocked position. They are robust and easy to operate.
Housing and Bolt Sizes: The housing is typically a sturdy metal case, and the bolt rod is usually a thick, flat piece of steel. The overall length can range from 100mm to 300mm.
Bolt Throw Length: The “throw” is the distance the bolt travels. A longer throw—typically 20mm to 30mm—provides a more secure lock as it engages deeper into the frame or keep. This is a critical dimension for security.
Installation Considerations: These bolts can be installed horizontally or vertically. For vertical installation on a gate, ensure the bolt is long enough to drop securely into a floor-mounted keep.
Flush bolts are mortised into the edge of a door, creating a clean, concealed look. They are almost exclusively used on double doors to secure the inactive leaf.
Standard Lengths: Common lengths include 150mm, 200mm, and 300mm. Longer bolts are easier to reach when installed on tall doors.
Body Depth & Mortice Size: The body of the bolt must fit within the door’s thickness. Standard body depths are around 15mm to 20mm, requiring a mortice of the same depth. The width is typically around 20mm.
Rod Throw Distances: The bolt rod needs to extend far enough into the header (top frame) and threshold (floor) to be secure. A minimum throw of 15mm is recommended.
Similar to flush bolts, concealed bolts are mortised into the door but are often operated by a hidden mechanism, like a small lever or a key.
Body Width & Depth: These are designed for a tight fit inside the door edge. The body is usually slim, with a width of 15-20mm and a depth that corresponds to the door’s thickness.
Rod Diameter and Stroke Length: The rod diameter is typically around 8-10mm. The stroke, or throw, is the distance the rod extends, usually between 15mm and 25mm.
Drop bolts are used to secure the bottom of a door or gate to the floor. They can be manual or electric.
Manual Drop Bolts: These are long, heavy-duty rods. Lengths often range from 150mm to 450mm or more, allowing them to be operated without bending down. The bolt shaft is thick, often 12mm to 19mm in diameter. They require a hole drilled into the floor for the bolt to drop into.
Electric Drop Bolts: These are used in access control systems.
Faceplate Dimensions: The faceplate that is mortised into the door frame is typically around 200-260mm long and 25-30mm wide.
Body Depth: The main body of the lock can be 40-50mm deep.
Bolt Extension: The bolt typically extends 15-20mm from the body.
The physical dimensions of a door bolt are not just about fit—they are the primary determinants of its strength.
Longer Bolts, Deeper Engagement: A longer bolt allows for a greater “throw,” meaning it engages more deeply into the door frame or keep. This makes it significantly harder to pry the door open.
Thicker Bolt Rods for Force Resistance: A thicker bolt rod is more resistant to being cut, bent, or sheared off during a forced entry attempt. A 12mm diameter bolt is substantially stronger than an 8mm one.
Plate Width and Screw Stability: A wider mounting plate with well-spaced, heavy-gauge screws distributes force across a larger area of the door and frame. This prevents the bolt from being ripped off under pressure.
Mortice Depth for Flush Bolts: For mortised bolts, a precise and sufficiently deep cut-out is crucial. A loose fit can compromise the bolt’s integrity, allowing it to be dislodged.
Heavy-Duty Dimensions: Heavy-duty bolts combine all these elements: thick rods, long throws, and large, reinforced mounting plates with multiple fixing points. These larger dimensions are what give them the strength to secure heavy gates and industrial doors.
Matching the bolt dimensions to the specific door type is essential for optimal performance and security.
Interior: For internal wooden doors like bathrooms or bedrooms, a 75mm or 100mm barrel bolt with an 8mm diameter is generally sufficient.
Exterior: For external wooden doors, a 150mm or 200mm heavy-duty bolt with a 10-12mm diameter rod and a wide mounting plate is recommended for added security.
These doors require robust hardware. Choose bolts with thicker rods (12mm+) and longer plates that can be securely fastened, often with bolts rather than screws, to prevent them from being easily pried off.
Aluminium doors are often slimmer. Straight bolts or slimline flush bolts with a body depth that fits the door’s profile are ideal. A 150mm or 200mm length is standard.
For sliding patio doors, hook bolts or specialized sliding door locks are more common. However, for a secondary sliding barn door, a surface-mounted sliding bolt with a long throw (25mm+) provides good security.
Flush bolts are the standard. Use a 150mm or 200mm flush bolt for both the top and bottom of the inactive door leaf. Ensure the rod throw is at least 15mm to engage securely with the frame and floor.
These require the most robust solutions. Use a heavy-duty drop bolt (300-450mm long) or a large sliding gate bolt with a diameter of 16mm or more. The goal is to anchor the heavy door securely to the ground or a solid post.
Follow these steps to ensure you select the correct dimensions for your project.
For mortised bolts like flush bolts, the door must be thick enough to accommodate the bolt’s body. A standard interior door (35-45mm thick) can typically house a flush bolt.
For surface-mounted bolts, ensure the door stile (the vertical part of the door) and the frame are wide enough to mount the bolt and the keep without splitting the wood.
For good security, aim for a bolt throw that engages at least 15-20mm into the door frame or floor. A deeper engagement provides much greater resistance to force.
For outdoor applications, choose bolts made from corrosion-resistant materials like stainless steel or hot-dip galvanized steel. Outdoor bolts should also have larger dimensions to withstand harsher conditions and higher security risks.
If you are securing a garage, a large gate, a workshop, or any area containing valuable items, always opt for heavy-duty dimensions. The thicker steel and more secure fixings are a worthwhile investment in security.
While a deadbolt lock is the primary security for a front door, a supplementary heavy-duty surface bolt of at least 150mm with a 12mm diameter can add an extra layer of security, especially if installed high on the door.
For double doors, 150mm or 200mm flush bolts are standard. This length provides enough leverage to operate the bolt comfortably while securing the inactive door at the top and bottom.
A bolt with a rod diameter of 12mm (approx. 1/2 inch) or more is generally considered heavy-duty.
A 50mm bolt is very short and offers minimal security. It is better suited for small cabinets or cupboards. For an interior door, a 75mm or 100mm bolt is a better choice for providing privacy.
To measure for a flush bolt, you need the bolt’s length, width, and depth. Mark the bolt’s outline on the door edge, then use a chisel or router to create a recess (mortice) that matches these dimensions exactly for a snug, secure fit.
Selecting the right door bolt is about more than just aesthetics; it’s a critical decision for security and functionality. The dimensions of the bolt—its length, thickness, and throw—directly determine its strength and suitability for a particular application. From a small barrel bolt for a bathroom to a heavy-duty drop bolt for a garage, every measurement matters.
By understanding the standard dimensions and matching them to your specific door type and security needs, you can ensure a secure, professional installation. Always remember that for areas requiring high security, investing in larger, heavy-duty dimensions is the most effective way to protect your property.
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