Reference:Cylinder

The cylinder statement creates a finite length cylinder with parallel end caps The syntax is:

CYLINDER:
  cylinder {
    <Base_Point>, <Cap_Point>, Radius
    [ open ][OBJECT_MODIFIERS...]
    }

The geometry of a cylinder.

Where <Base_Point> and <Cap_Point> are vectors defining the x, y, z coordinates of the cylinder's base and cap and Radius is a float value for the radius.

Normally the ends of a cylinder are closed by flat discs that are parallel to each other and perpendicular to the length of the cylinder. Adding the optional keyword open after the radius will remove the end caps and results in a hollow tube.