This part of ISO 5414 lays down the dimensions of tool chucks (end mill holders) with clamp screws designed for driving flatted cylindrical shanks in accordance with ISO 3338-2 and specifies the clamp screws used. It also gives the maximum diameter of the chuck nose. This part of ISO 5414 defines two types of drive: - chucks with bores of d1 u 20 mm intended for driving cylindrical shank tools with a single flat, these tools being provided with either a single or a double cutting part; - chucks with bores of d1 W 25 mm intended for driving cylindrical shank tools with a double flat, these tools being provided with a single cutting part only. NOTE The connecting dimensions of the various types of chucks and the designation of tool chucks (end mill holders) with clamp screws are dealt with in ISO 5414-2.