Why so (National) Fine?

by admin on December 10, 2017

Why National Fine (NF) as opposed to National Coarse (NC) when using threaded fasteners?


The reason is strength. If you compare the strength of similarly sized fasteners, the one with National Coarse (NC) versus National Fine (NF) threads, you’ll see that the NF threaded fastener is between 10% and 20% stronger than the NC version. As rule of thumb, the NF part is about 15% stronger than the NC part.

Why not just go with a larger fastener?
Your part is likely constrained in size of penetration that it can accept or the size of the fastener would interfere with adjacent parts. In the case of my large screen LCD set, I don’t know why as the piece that they threaded was in no way limited in size. Similarly, the case mold could have been increased in size to take care of the increased fastener size. I think it was likely an oversight on their part and they chose to increase the strength by changing the thread pitch instead of remaking the mold… Just a guess on my part. Thankfully, the legs were made out of aluminum so it was relatively quick to drill and tap the threads in the piece.

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