Round Head Coach Bolt

The alloy steel that has undergone heat treatment is selected. The Xiaoguo® wholesale round head Coach bolt has a performance grade of 10.9 and an ultimate tensile strength exceeding 1000 MPa. It is suitable for heavy machinery, bridges and high-load structures.

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Product Description

round head Coach bolt (a type of carriage bolt) and Carriage bolt belong to the same product category. The main difference lies in the regional names: in North America, it is commonly called Carriage bolt, while in Commonwealth countries (such as the United Kingdom, Australia, and New Zealand), the term round head Coach bolt is more commonly used. It is a fastener with a semi-spherical head (round head) and a square anti-loosening structure at the bottom of the neck, specifically designed for single-side installation.

Structural Characteristics

The structural design of round head Coach bolt is centered around the core goal of "single-side installation and automatic anti-tipping", and it is mainly composed of the following four functional parts:

（1）Head

Shape: Hemispherical (round head) or flat-top round head. The surface is smooth, without any tool interfaces such as hexagonal, square or cross slots.

Function and Purpose:

Provide a large area of load-bearing surface

Aesthetics and Security

Smooth and rounded design

（2）Neck (Neck) - The Most Crucial Anti-Slip Structure

Shape: Located directly below the head, it is square (Square) or ribbed square (Ribbed Square).

Function and Purpose:

Mechanical anti-turning function

No need for auxiliary tools

Precise positioning

Round Head Coach Bolt

Mon	M5	M6	M8	M10	M12	M16	M20	M24
P	0.8	1	1.25	1.5	1.75	2	2.5	3
dk max	11.3	13.5	18	22.5	27	36	45	54
dk min	10.2	12.4	16.9	21.2	25.7	34.4	43.4	52.1
ds max	5.48	6.48	8.58	10.58	12.7	16.7	20.84	24.84
ds min	4.52	5.52	7.42	9.42	11.3	15.3	19.16	23.16
k max	3.2	3.6	4.8	5.8	6.8	8.9	10.9	13.1
k min	2.5	3	4	5	6	8	10	12
r max	0.5	0.5	0.5	0.5	1	1	1	1.5

（3）Shaft section (Shank / Unthreaded Portion)

Shape: Located between the neck and the threads, it is a smooth cylindrical shaft with a flat surface and no threads.

Length: It is calculated by subtracting the thread length b from the total length L of the bolt. Different specifications have standard ratios.

Function and Purpose:

Withstanding shear load

Precise positioning

Avoiding the application of force on the threads

（4）Threaded Portion

Shape: Located at the end of the round head Coach bolt, it is a standard metric coarse thread (ISO) or an American standard UNC thread.

Length (b):

Standard stipulates: When L ≤ 125mm, b ≈ 2d + 6mm (d is the nominal diameter); when L > 125mm, b ≈ 2d + 12mm.

The thread length of the actual product can be extended according to the customer's requirements (customized full thread).

Function and Purpose:

Generate clamping force by cooperating with the nut

Adjust the preload force

Structural Comparison

The advantage of round head Coach bolt lies in its unique structure. So, compared to other types of bolts, what are the differences? Please take a look at the following table and you will discover!

Comparison items	round head Coach bolt	hexagonal head bolt	internal hexagonal bolt
Head shape	Hemispherical round head	hexagonal	cylindrical head with internal hexagonal hole
Anti-loosening method	Mechanical anti-loosening with square neck	requires fixing the head with a wrench	requires using an internal hexagonal wrench to fix the head
Number of installers	1	2	1
Can be pre-drilled?	Yes	No,	No,
Typical applications	Wood, outdoor furniture, fences	Steel structure, mechanical assembly	Precision machinery, molds