OS-1 Operating Stand
The OS-1 provide a convenient & accurate way to perform repeated hardness tests. The stand provides the correct testing pressure as noted in ASTM D-2240 , thus eliminating human erroe.
The OS-1 may be used with durometer types  A , D , B , C , DO , O , OO , OOO and E .

OS-2  & OS-4 Operating Stands
Smaller versions of the OS-1 stand, the OS-2 & OS-4 provide a convenient & accurate way to perform repeated hardness tests. All stand provide the correct testing pressure as noted in ASTM D-2240 , thus eliminating human errors . The OS-2 can be used for type A , B , O & E , while the OS-4 is for use with types  OO & OOO

OS-2H, OS-3 & OS-4H
The OS-2H, OS-3 & OS-4H offer all the features of the standard REX OS-2 & OS-4 stands, plus a dampening feature. The dampener lowers the durometer  at the same rate for each test , resulting in superior repeatability  for all durometer tests ( especially in the sensitive OO , OOO and M durometer types ). 
The OS-2 can be used for durometer types A , B , O & E.
The OS-3 is used only for type M durometers, and is ideal for o - ring  testing ( o-ring fixtures are available ) . 
The OS-4H is for use with the OO & OOO durometer types.