This International Standard specifies the dimensions of metric internal cruciform ribbed drives used in metric screws in the nominal thread diameter range of 3 mm to 20 mm. Drivers and gauges used in conjunction with these drives are defined in ISO 14280 and ISO 14281.
GSO ISO 12256:2013 history
2013GSO ISO 12256:2013 Aerospace -- Drives, internal, cruciform, ribbed -- Metric series