Discount Musical instruments - By 2Kool4Skool

  here is how to place the bridge in the proper location:

• Loosen the strings slightly, so that you won't scratch the head while you are moving the bridge around.
  
• using a yard stick or ruler, measure from the nut to the middle of the 12th fret. 
  
• If you don't have a yardstick handy, you can use a piece of wood, and mark it at the 12th fret.
• measure that same distance from the 12th fret to the banjo head and make a small pencil mark on the head at that distance, and place the bridge there.  It's now in the general location.
• Tune the instrument to standard tuning, using your ear, or an electronic tuner.
• fine tune the placement. Play each string open, and then freted at the 12th fret.
• Using your ear, determine if the fretted note is higher or lower than the open note. 
  
• If the fretted note is higher, (sharp) the bridge is too close to the neck and needs to move toward the tailpiece. 
  
• If the fretted note is lower, (flat) the bridge needs to be moved toword the neck. 
  
• If you measured correctly in step 2, these movements should be very slight.  Possibly only 1/16 of an inch or so.