what the code "M" in the LT1761 part number means?

What is the difference between the following part numbers?
LT1761ES5-3.3#TRMPBF
LT1761ES5-3.3#TRPBF
Yes, I know one part number has the M and and the other does not.
The M is not mentioned in the datasheet.
What does the M designate?

This is actually calling out a mini-reel from the factory. No difference in the actual part just the packaging.

-Robert