However, this term was later replaced with UNC, or Unified National Coarse, to effectively explain the thread design. However, many will still refer to coarse threaded bolts as being USS and will also believe that the USS flat washer is indicated to be used with the 'USS' coarse threaded bolt. As we will later on see, this is not the case and is inaccurate for lots of applications. The USS flat washer was first established in the early 19th century for applications involving compressible products, such as wood, thin sheet metal, and so on. The outside diameter was wide sufficient to provide a big surface area to avoid embedment of the bolt head into the material and lessen joint compression, while the within size was large enough to accommodate bolts with extremely loose tolerances for handmade bolts of that era.
For that reason, the smaller sized, more compact SAE flat washer was developed and called after the Society of Automotive Engineers. The Latest Info Found Here within diameter of the SAE flat washer is much closer to the size of the size of bolt it is to mate with given that the bolts these days are all manufactured to close tolerances by machine from cold forming to hot heading. The outside diameter of the SAE flat washer is also smaller sized as it does not require to supply for a large load bearing area to prevent compression, as did the USS washer against compressible materials. Figure 1 illustrates the dimensional differences in between the same internally sized flat washers: The USS flat washer is on the left, and the SAE flat washer is on the right.
The typical idea was to pair the USS flat washer with the coarse (USS) threaded bolt and the SAE flat washer with the great thread (SAE) bolt. This is not constantly the very best situation to follow, particularly when using greater strength fasteners such as Grade 8 (10. 9) and even Grade 5 (8. 8), as this practice might ultimately lead to failures in high strength joints. PRODUCT STRENGTH For steel flat washers, there are two choices: plain or solidified. Flat washers are not designated by grades, per se, with the exception of structural washers under the ASTM (American Society for Testing and Products) Standard F436.
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