Class 8.8 Square Head Bolt

Bulk purchase of Xiaoguo® stainless steel Class 8.8 square head bolt. These bolts have strong corrosion resistance, with a salt spray test duration exceeding 1000 hours. The products are rust-proof for a lifetime and can save maintenance costs. Full-size inventory is available.

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Product Description

Principles for material selection

When selecting the material for Class 8.8 square head bolt, the key lies in achieving the best balance while meeting the strength and toughness standards, based on the bolt specifications, application environment, and cost.

（1）Material category

Medium carbon steel (such as 35K/SWRCH35K): Standard specifications with a diameter of ≤ M16, offering high cost-effectiveness and being the most commonly used in industrial applications.

Alloy steel (such as 40Cr/42CrMo): Larger specifications with a diameter of ≥ M20, featuring better hardenability.

（2）Surface treatment

Blackening/Phosphating: Avoids hydrogen embrittlement risk and is the safest surface treatment for Class 8.8 square head bolt and above high-strength bolts.

Electro-galvanizing: Only applicable in normal environments.

Dacromet/Zinc-Aluminum Coating: Suitable for scenarios with high requirements for corrosion prevention (such as automobiles, wind power)

Class 8.8 Square Head Bolt

When choosing materials, it is recommended to follow the following approach:

（1）Small-sized bolts (M5-M12): Preferentially use 35K or 1038 medium carbon steel. After cold heading, they undergo heat treatment.

（2）Large-sized bolts (M14-M64): These should be made of alloy steel such as 40Cr or 35CrMo.

（3）Key structural parts: Preferentially use 35CrMo or 42CrMo alloy steel to ensure long-term reliability under harsh conditions.

Heat treatment process

（1）Quenching: Heat the Class 8.8 square head bolt to above the critical temperature (approximately 850 - 870°C), then rapidly cool them (either oil quenching or water quenching) to transform the steel structure into martensite, thereby achieving high strength.

（2）Tempering: Reheat the bolt that has undergone quenching to approximately 425-500°C, hold it for a while, then cool it down. This process adjusts the hardness, enhances the toughness, and ensures the optimal balance between strength and toughness.

（3）The key role of heat treatment: The tensile strength of carbon steel bolts without heat treatment is usually less than 500 MPa. After quenching and tempering treatment, it can be stabilized at over 830 MPa.

Class 8.8 Square Head Bolt

Mon	3/8	7/16	1/2	5/8	3/4	7/8	1	1-1/8	1-1/4	1-3/8	1-1/2
P	16\|24\|32	14\|20\|28	13\|20\|28	11\|18\|24	10\|16\|20	9\|1420	8\|1220	7\|12\|18	7\|12\|18	6\|12\|18	6\|12\|18
ds max	0.388	0.452	0.515	0.642	0.768	0.895	1.022	1.149	1.277	1.404	1.531
s max	0.562	0.625	0.75	0.938	1.125	1.312	1.5	1.688	1875	2.062	2.25
s min	0.544	0.603	0.725	0.906	1.088	1.269	1.45	1.631	1.812	1.994	2.175
e max	0.795	0.884	1.061	1.326	1.591	1.856	2.121	2.386	2.652	2.917	3.182
e min	0.747	0.828	0.995	1.244	1.494	1.742	1.991	2.239	2.489	2.738	2.986
k max	0.268	0.316	0.348	0.444	0.524	0.62	0.684	0.78	0.876	0.94	1.036
k min	0.232	0.278	0.308	0.4	0.476	0.568	0.628	0.72	0.812	0.872	0.964
r max	0.03	0.03	0.03	0.06	0.06	0.06	0.09	0.09	0.09	0.09	0.09
r min	0.01	0.01	0.01	0.02	0.02	0.02	0.03	0.03	0.03	0.03	0.03

Packaging Introduction

The packaging of Class 8.8 square head bolt is of a multi-layer structure, divided into three levels from the inside out: inner packaging, outer packaging, and pallet fixation, forming a complete protective layer.

（1）Inner packaging

Plastic bags (PE bags): 5kg per bag, 10kg per bag, 25kg per bag. Generally, they are bulk industrial packaging.

Small boxes: 5kg small boxes, 4 boxes in one large box, suitable for medium and small batch orders

Brand small packaging: 6 pieces per box, 10 pieces per box, 20 pieces per box, for DIY retail and home hardware products

（2）Outer packaging

Corrugated carton: 25kg per box, 36 boxes per pallet. Standard export packaging.

Strengthened carton: Can be customized according to customer requirements. For heavy or special-sized products.

（3）Tray

European standard pallets / glued board pallets: approximately 900kg - 1000kg per pallet. For container shipping and forklift handling.