Choosing the correct replacement Mortise Handle:
When selecting a replacement Mortise
Handle, it is important to know whether you have an "A" position or
"B" position handle set.
"A" position handles will have the thumbturn located directly in the
center between mounting holes,
while the "B" position handles will have the thumbturn located
off-center, closer to the bottom mounting hole.
It is also important to take accurate measurements of your existing handle,
before trying to select a replacement.
The most important measurement is the distance center-to-center between screw
holes. It is also helpful to know the width and length of the handle, and the thickness of the door.