NAMUR standard is the interface standard (VDI/VDE3845-2010) for actuators, specified in VDI (German Institute of Engineers Standards) and VDE (German Institute of Electrical Engineers Standards).
This standard is adopted mainly in Europe and America.
It is adopted for the pneumatically operated ON-OFF actuators (*), the solenoid valve of this standard can be connected without brackets.

(*Some actuators are not supported.)