|Serial number||NMI-23"NMI" can not be assigned to a declared number type with value -23.|
- 23. Double geophone construction by Mandrel Industries. Two part plastic case is secured by knurled screw-on rings at each end. Stainless steel clamp further secures case and contains, at bottom, a threaded stud for coupling attachment. Case is filled with silicone rubber. Plastic case is stamped with name MANDREL INDUSTRIES and Mandrel logo.