Screw Definition and 6 Discussions

A screw and a bolt (see Differentiation between bolt and screw below) are similar types of fastener typically made of metal, and characterized by a helical ridge, known as a male thread (external thread). Screws and bolts are used to fasten materials by the engagement of the screw thread with a similar female thread (internal thread) in the matching part.
Screws are often self-threading (also known as self-tapping) where the thread cuts into the material when the screw is turned, creating an internal thread that helps pull fastened materials together and prevent pull-out. There are many screws for a variety of materials; those commonly fastened by screws include wood, sheet metal, and plastic.

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  1. P

    Minimum screw thread engagement to support weight?

    Hello All, I know there are rules of thumb and thread engagement calculators online but I am trying to find mathematically what the minimum number of threads acceptable would be. I currently have an eyebolt that will be torqued to a specific value. This eyebolt setup will then need to lift a...
  2. CynicusRex

    Appropriate tightness of bolts between skateboard and trucks

    As you can see in the pictures below the trucks are attached to the skateboard with four screws nuts and bolts, with a 2~3mm piece of rubber between the truck and the board. I've always wondered if tightening the screws bolts harder, decreases or increases the strength of the 7-layered plywood...
  3. Justin71

    Screw ball torque

    Hi I don't understand what Fa mean ? This the weight or no ? And i don't understand too why in the torque TL, we have an additional part with the preload, the internal friction coeff of preload nut ... What is it ? Thanks.
  4. Wrichik Basu

    Why does it get harder with time to rotate a screw?

    A couple of forces act on the screw and create the turning effect. But after sometime it gets harder. So, net torque is decreasing, but why is it decreasing? Frictional force comes into action, but friction doesn't depend on surface area. So, frictional force will remain constant. So what...
  5. carb

    Contact pressure - screw pretension

    Hello, I'd like to calculate the max contact pressure in the below assembly, just before contact loss between the beam and the wall. The beam is clamped to the wall with a pretensioned screw, and sustaining a force at his gravity center. I'm assuming all bodies dimensionnaly stable (no...
  6. M

    Proper Screw Threading Design

    Hi, My question regards a plastic bottle that I'm designing. For the threading that fits the two parts together, will and Acme thread work? This is how I've designed my part, but I can change the thread profile if need be. Also, is there anything that I need to know regarding the pitch? I have...