8 mm probes provide a thicker encapsulation of the probe coil in the molded PPS plastic probe tip. This results in a more rugged probe. The larger diameter of the probe body also provides a stronger, more robust case. Bently Nevada recommends the use of 8 mm probes when possible to provide optimal robustness against physical abuse.
A 3300 XL Proximitor Sensor is available and provides numerous improvements over the non-XL version. It is electrically and mechanically interchangeable with the non-XL version, and is recommended as best available technology for most applications.