A link to a page about flanges, quite a good overview to explain
what they are to the layman.
This information is provided "as is" and pipingdesigners.com makes
no warranty of any kind with respect to the subject matter or accuracy of
the information contained herein. pipingdesigners.com specifically
disclaims all warranties, expressed, implied or otherwise, including without
limitation, all warranties of merchantability and fitness for a particular
purpose. In no event shall pipingdesigners.com be liable for any special,
incidental, indirect or consequential damages of any kind or any damages whatsoever
resulting from loss of use, data, profits, whether or not advised of the possibility
of damage, and on any theory of liability, arising out of or in connection
with the use of the information contained herein. This publication may include
technical inaccuracies or typographical errors. Changes may be periodically
made to the information herein.