ER collet chucks with CAPTO (CPT) interface are modular tool holders designed to mount ER collets according to DIN ISO 15488 (DIN 6499) on machine tools equipped with a CAPTO interface compliant with DIN ISO 26623-1. They combine the speed and rigidity of the CAPTO system with the versatility of ER clamping, allowing straight-shank tools to be gripped uniformly over 360° by means of collet and nut, resulting in stable and repeatable clamping whenever precision and fast tool change are required.

The CAPTO coupling, thanks to its polygonal connection, provides high torsional rigidity and reliable positioning repeatability, which translates into improved machining safety and more dependable torque transmission compared with many traditional solutions. It is a common choice on multitasking centers and CNC lathes with modular systems, where production continuity and reduced setup times matter as much as accuracy.

On the collet side, the ER family covers a wide diameter range with only a few components and is well suited for operations such as drilling, tapping, reaming and light-to-medium milling, especially when using standard straight-shank tools. Versions can differ by the nut: depending on the setup it can be standard or hexagonal profile, which helps tightening with common wrenches or in more restricted spaces.

Compared with other interface standards such as ISO, BT/SK or HSK, the CAPTO solution is preferred when the goal is a modular, easy-to-handle and highly rigid system, while maintaining the operational flexibility typical of ER collets, which remain among the most practical solutions for precise and repeatable clamping of cylindrical tools.