Metric ISO Threads: Concept, Dimensions, and Tolerances

Tolerances are very small in screw manufacturing. Terms and fitting systems can be difficult to understand. At the same time, thread dimensions and profile accuracy are crucial for determining important factors, such as

• whether a coating can still be applied to the screw thread
• whether the parts to be joined can be screwed together on assembly without difficulty or the need for reworking
• whether the thread can transmit the forces for which the components were dimensioned

To help answer these questions, we have put together the following information on ISO metric threads, their dimensions and tolerances.

Contents

• General information about the use of the material
• Basic concept and nominal dimensions according to ISO 724
• Clearance fit on metric ISO threads according to ISO 965
• Tolerance fields for commercial screws and nuts
• Limits for metric (standard) coarse threads
• Selection series for coarse threads according to ISO 262
• Limits for metric fine threads
• Selection series for fine threads
• Permissible tolerances for plastic fasteners