JB/T 9987-1999
Diameter of the twist drill used before tapping (English Version)
- Standard No.
- JB/T 9987-1999
- Language
- Chinese, Available in English version
- Release Date
- 1999
- Published By
- Professional Standard - Machinery
- Status
- 2010-02
- Latest
- JB/T 9987-1999
- Scope
- This standard applies to the diameter of twist drills used for drilling holes before tapping ordinary threads (according to GB/T 192～193, GB/T 196～197). The diameters of twist drills listed in this standard are suitable for drilling under general production conditions. Depending on the production conditions, similar sizes can be selected in the twist drill standard series according to actual needs. Within the tolerance range of the small diameter of the threaded hole, it is recommended to use a larger-sized twist drill as much as possible to reduce the load of the tapping process and improve the life of the tap. The diameter of the twist drill listed in this standard is basically calculated according to the following formula: d=DP where: d——the diameter of the twist drill; D——the nominal diameter of the thread; P——the pitch.
JB/T 9987-1999 history
- 1999 JB/T 9987-1999 Diameter of the twist drill used before tapping
