Scotty cameron 1.5, 2 or 2.5?

In the Newport range, .5 means the putter has a flow neck (curved). Others without .5 have a plumbers neck.

1.5 and 2.5 have differences in the shape of the sole and bumpers.

Both aspects are largely aesthetics. Some would say that the flow neck is more suitable to a stroke where you open and close the face, and plumbers neck to a straighter back-through stroke.