INTRODUCTION This Data Item presents a procedure for assessing the suitability of a user-specified commercial needle-bearing roller follower driven by a disc cam. The choice of an appropriate roller follower is an important step in the design of cam systems used in many industrial machines and the use of the procedure presented in this Item@ in conjunction with a suitable manufacturer's catalogue@ will ease this choice. A decrease in design time can be achieved together with improvements in life@ load/speed capacity and hence machine reliability. Cam roller followers are subject to conditions of continuously varying angular velocity and load during operation. To assess the performance of a given roller it is necessary to determine@ at a series of cam angular positions@ the values of load and velocity and then@ using the method recommended in manufacturers' catalogues@ to convert them to equivalent load (see Equation (3.46)) and equivalent velocity (see Equation (3.45)). This analysis is carried out by a computer program (see Section 7) supplied with this Data Item. The program determines the estimated life@ the maximum contact force at the cam oller interface@ the maximum load on the roller stud or spindle and the maximum angular velocity of the roller. These values are then used to assess the suitability of the chosen roller.