Stop Using the Wrong Washer: F436 vs. SAE USS Explained

Quick Summary:
Choosing the wrong washer can cause 80% of structural joint failures. ASTM F436 and F436M are high-strength washers made from medium carbon steel, heat-treated to 38-45 HRC. They range from 1/4" to 4" in inner diameter. In contrast, standard SAE and USS washers are made of ordinary carbon steel with lower hardness (100HV) and cover a wider size range (0 to 4"). F436M is the metric equivalent. For safety-critical structural connections, always choose F436/F436M over standard SAE USS washers.
 

When a structural bolted joint fails, 80% of the time it's due to the wrong washer choice. So, what makes ASTM F436 so special compared to the standard SAE washers you use daily?

The differences between ASTM F436 and ASTM F436M flat washers and other common American standard flat washers are mainly reflected in the selection of materials, differences in mechanical properties, differences in product sizes, application occasions, and certification standards. A deep understanding of these differences is essential to ensure the reliability and safety of fastener connections.

1. From the perspective of material selection and mechanical properties: Most of the materials of F436 and F436M flat washers are made of medium carbon steel sheet metal for stamping (common materials include S45C, S50C, S55C, S60C and other steels, in addition, they can also be made of stainless steel, copper, aluminum and other materials). After forming, they need to be heat treated and hardened. The hardness after hardening is 38-45HRC Rockwell hardness. The hardness of the washers after hot-dip galvanizing can be 26HRC-45HRC Rockwell hardness. This treatment process enables F436 and F436M flat washers to maintain high stability and durability when subjected to complex mechanical environments such as pressure and shear force. The American standard ordinary flat washers ANSI/ASME B18.22.1 SAE type and ANSI/ASME B18.22.1USS type are normally made of ordinary carbon steel, with a normal hardness of 100HV Vickers hardness. If hardening is required, it can be made of different materials and heat treated to achieve the required hardness value, such as 140HV, 200HV, 300HV, etc.

Use in		3	3-1/4	3-1/2	3-3/4	4
d		3-1/8	3-3/8	3-5/8	3-7/8	4-1/8
dc		5-1/2	6	6-1/2	7	7-1/2
h	Max	0.34	0.34	0.34	0.34	0.34
	Min	0.24	0.24	0.24	0.24	0.24
n	Min	2-5/8	2-7/8	3-1/16	3-5/16	3-1/2

 d: Inner diameter of washer; dc: Outer diameter of gasket; h: Thickness of washer

3. Differences in product usage and certification standards: F436 and F436M high-strength hardened flat washers are usually used in conjunction with high-strength bolts ASTM A325, A325M, A490, and A490M, with reference to the American standard ASTM B 18.2.6. American standard flat washers are mainly used for daily fastener connections, mainly with reference to the American standard ANSI B 18.22.1. F436 and F436M flat washers are widely used in various fields such as construction, aviation, automobiles, and heavy machinery due to their high strength. In construction and bridge engineering, F436 washers are used to connect steel structures and concrete structures to ensure the stability and safety of the joints. In the aviation and automotive fields, F436 washers are used to connect engines, chassis, and other components to ensure safety and reliability. The hot-dip galvanizing treatment of F436 and F436M flat washers can effectively resist corrosion and extend their service life. In addition, F436 and F436M flat washers are also commonly used in the combination of A325 structural screws, studs and nuts to meet the strict requirements of fasteners in building structure design. Other types of flat washers may not be competent in certain specific occasions due to limitations of materials, performance and other factors.

In summary, F436 and F436M flat washers have significant differences from other flat washers in terms of material selection, mechanical properties, size standards, usage scenarios, and certification standards. These differences give F436 and F436M flat washers unique advantages and broad application prospects in the field of fastener connections. When selecting flat washers, these factors need to be considered comprehensively based on the specific application scenario and usage environment to ensure that the selected flat washers can meet the design requirements and usage needs. At the same time, it is also necessary to pay attention to choosing manufacturers with good reputation and strong technical strength to cooperate with, so as to ensure that the quality and performance of the purchased flat washers meet the expected level. Only in this way can the reliability and safety of the fastener connection be ensured, providing solid protection for various projects and equipment.

FAQ
1. What is the hardness of ASTM F436 washers?
   A: 38-45 HRC (26-45 HRC after hot-dip galvanizing).
 

2. What material is used for F436M washers?
   A: Medium carbon steel (S45C, S50C) or stainless steel.
 

3. What is the main difference between SAE and USS washers?
   A: SAE washers are thinner and have smaller outer diameters than USS washers.
 

4. What is the inner diameter range of F436 washers?
   A: From 1/4 inch to 4 inches.
 

5. Are SAE USS washers heat treated?
   A: Normally not; they are ordinary carbon steel (100HV).