# Is outside diameter the same as circumference?

1. Jan 13, 2014

### bcrary3

Okay, this might be a stupid question, but I have a sheet with all the formulas to find all kinds of anything you'd need to find about a gear. However I am confused by when it says outside diameter. Is outside diameter the same as circumference?
How do I find outside diameter using either the radius or diameter of the circle?

Thanks!

2. Jan 13, 2014

### phinds

There is this really marvelous facility on the Internet called Google Search. You should learn how to use it. I'll bet a Google entry of define "outside diameter" will tell you what you want to know.

3. Jan 17, 2014

### Physics_Kid

just as easy to also post the answer to newb Q, and then foster use of Gool or the like.

OP, no, OD is just that, the OD of say diameter of a pipe (the circular cross section after cutting the pipe perpendicular to its radial axis). mostly everything is 3D, thus a tube has a ID due to wall thickness.

Circumferene = 2πr = πd

4. Jan 17, 2014

### gmax137

Gear specifications have several different diameters, since the gear teeth are along the radius. So there's a diameter at the base of the tooth, at the outside edge of the tooth, along the line of action (where the meshing teeth touch) etc. Look at a gear manufacturer's website for a drawing and the definitions for the type of gear you're interested in.

Or try this:
https://en.wikipedia.org/wiki/Standard_pitch_diameter#Standard_pitch_diameter

Last edited: Jan 17, 2014
5. Jan 17, 2014

### Physics_Kid

my bad, didnt see the gear piece.

are they like threading guides, a minor and major diameter, w/ different designation for external vs internal threads (teeth in the case)?

6. Jan 17, 2014

The outside diameter of a gear is just the diameter at the tips of the teeth. They specify "outside" in order to differentiate from things like the pitch diameter and the root diameter.

7. Jan 18, 2014

### Baluncore

8. Jan 20, 2014

### bcrary3

Thanks for the help everyone! :D