In order to determine the appropriate clamping rail you need to look for the model number (507 or 508) and the model variant on the nameplate.

The nameplate can be found on the underside of the machine.

The model variant number for the old version: 00.06.xxxxx

The model variant numbers for the new versions:
00.16.xxxxx                                                                                                                                                             00.26.xxxxx
00.36.xxxxx
00.46.xxxxx
00.56.xxxxx
00.66.xxxxx

These new version numbers apply to only two rails: one for model 507 and one for model 508.