Toy train operating and collecting

What is meant by 0-31 track ?

 The diameter of a circle of this track is 31 inches.  O27 is 27 inches, etc.

wyomingscout

 Yes, Wyomingscout is right,whenever it is 0-anything it denotes the Diameter that a circle of that curvature would create. But it is a little more complicated than that because 027 and Standard O Gauge,which is often refered to as 031 because that is the smallest curve in that type, have different profiles.

  027 track has a lower rail and tie cross section and has smaller diameter connecting pins and is available in 027, 042, 054 and K Line made 072 curves, in 027 profile. Switches are available in 027 and 042 diverging curves.

  Standard O Gauge has 031, 042, 054 and 072 curves as well, and 031 042(IIRC) and 072 switches.

There are other companies besides Lionel that offer track and switches in those as well as other curveatures, such as Gargraves and Ross Custom Switches (RCS) being two of the best known.

  When discussing 027 or 031, it is important to know what the context is, are you discussing the actual curvature, or the track profile.

Doug

Is it correct to assume the diameter is measured by the center rail of the track?

O31 (originally called O and sometimes called O30) track is 30.534 inches in diameter to the outside ends of the ties.  The ties are 2 1/4 inches long; so the diameter to the center rail is 28.284 inches and the radius is 14.142 inches.

to the form the. other posts hit the nail on the head.

Couldn't get link to work, so deleted the post. See lionelsoni's post directly below.

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http://cs.trains.com/trccs/forums/p/123642/1403347.aspx#1403347

Here's a more recent topic:

http://cs.trains.com/trccs/forums/t/157853.aspx