This document specifies, with reference to the ISO230 series, some families of tests for accessory spindle heads used on machining centres or numerically controlled milling machines, etc., where applicable, with horizontal spindle (i.e. horizontal Z-axis). The tests considered in this document are also applicable to manual indexing heads.This document establishes the tolerances or maximum acceptable values for the test results corresponding to general purpose and normal accuracy spindle heads used on different types of machines.This document specifies several sets of procedures for geometric tests which can be carried out on different types of spindle heads for comparison, acceptance, maintenance, adjustments or any other purpose.Grinding heads and facing heads are not included in the scope of this document.This document deals only with the verification of geometric and positioning accuracy of the accessory spindle heads and does not apply to: the testing of the machine’s head(s) operation (e.g. vibration, abnormal sound noise level, stick slip motion of components); the machine’s spindle head(s) characteristics (e.g. speeds, feeds and accelerations) which are generally checked separately; or the verification of the machining capability under power. Tests concerning the accuracy of finished test pieces are dealt with in other ISOstandards.