As of Dec 2006 all Trilogy positioners using the magnetic encoders are using the PLME. Units before Dec 2006 used the LME. There is a mounting difference change.
If it is black and the mounting holes are on the top, then it is the 5um LME. The part number would be LME5F-XX where XX is the length in meters.
If it's black and the mounting hole pattern is diagonal, it's the 5um PLME. The part number would be PLME5F-XX where XX is the length in meters.
If the readhead is blue, it would be a 1um LME. The part number would be LME1F-XX where XX is the length in meters.
Color codes and phasing are the same. As the mounting is different, the bracket that the readhead has a different mounting pattern. For this reason it is best to inspect the readhead's mounting pattern and confirm this before purchasing. Because the mounting pattern is different, the PLME shouldn't be considered a dropin replacement for the LME.
LME and PLME Mounting Dimensions