What Does #4-40 Screw Mean?

When we first came into contact with the fastener industry, we basically didn’t know what the #4-40 screw stands for. I believe many of my friends will have such questions.

#4-40 screw indicates the diameter of the thread, and 40 indicates the number of teeth in the 25.4 mm. When the customer said that it is a #4 screw, but did not give the number of teeth, this must be confirmed with the customer. Because the #4 screw can have coarse and fine teeth. When it is a coarse tooth, the thread diameter is 2.695 mm – 2.824 mm. When it is a fine tooth, the thread diameter is 2.713 mm – 2.827 mm. The #4-40 screw is coarse thread.

If you want to customize #4-40 screw, please send an email: annie.li@szsst88.com