In article .com,
"Bob" wrote:

I have the good fortune to own and use a Porter Cable 556
biscuit jointer. I would like to use FF biscuits and have
noticed that PC makes a 2" 4-tooth blade with a 7/8"
arbor for the newer model 557 jointer. Has anyone used
the 2" blade on their 556 jointer? I hate to spend
$50 on a blade that won't work.

My understanding is that the amount of travel in the sliding part is
insufficient for the small blade to reach out far enough for a complete
plunge. I am reasonably certain that it was the 556 which was under
discussion at the time. It is also the reason why the FF blade won't
work with other machines.
A quick check with a tape measure will verify that.