Both types are encoder versions with stainless-steel housings.
The "61" types are fitted with a solid, rugged stainlessâ€steel cover connected to the stainlessâ€steel flange. Standard cable fittings are made of nickelâ€plated brass.
=> This design allows complex encoder versions, such as absolute encoders with bus covers and types that require protected access to the interior of the encoders, (e.g. dip switches).
The "59" types include a deepâ€drawn stainlessâ€steel cover with a crimped stainlessâ€steel flange connection. Standard cable fittings are made of PVC.
=> This design is generally less expensive (although offering reduced variety of encoder versions): incremental encoders with cable connections, absolute encoders with cable connection and sealed cover (e.g. singleturn parallel, SSI or Interbusâ€S).