What is BS EN IEC 60191-1 - Mechanical standardization of semiconductor devices about?  
BS EN IEC 60191-1 is an international standard that covers the mechanical standardization of semiconductor devices.
BS EN IEC 60191-1 gives guidelines on the preparation of outline drawings of discrete devices, including discrete surface-mounted semiconductor devices with a lead count of less than 8.
Note: Additional details of reference letter symbols used in this document are given in Annex A.
Who is BS EN IEC 60191-1 - Mechanical standardization of semiconductor devices for? 
BS EN IEC 60191-1 on preparation of outline drawings of discrete devices is relevant to: 
- Manufacturers of semiconductor devices
- Product designer engineers
- Technical consultants
- Mechanical engineers
Why should you use BS EN IEC 60191-1-Mechanical standardization of semiconductor devices?  
Device outline drawing is a drawing that includes all dimensional characteristics required for the mechanical interchangeability of the complete device. The device outline drawing includes the case or body, all terminals and the locating tab if present.
The primary object of these drawings is to indicate the space to be allowed for devices in equipment, together with other dimensional characteristics required to ensure mechanically interchangeability. The international standardization represented by these drawings, therefore, encourages manufacturers of devices to comply with the tolerances on the drawings in order to extend their range of customers internationally.
BS EN IEC 60191-1 also gives equipment designers an assurance of mechanical interchangeability between the devices obtained from suppliers in different countries, provided they allow the space in their equipment that is indicated by the drawings and take note of the more precise information on bases, studs, etc.
What’s changed since the last update?
BS EN IEC 60191-1:2018 supersedes BS IEC 60191-1:2007 2007, which is withdrawn. BS EN IEC 60191-1:2018 includes some technical changes with respect to BS IEC 60191-1:2007. These include: 
- The Scope has been extended to include surface-mounted semiconductor devices with a lead count of less than 8
- A definition of the term "stand-off" has been added
- The methods for locating the datum have been extended to be suitable for SMD-packages
- The visual identification of terminal position one for automatic handling has been clarified
- The rules for the drawing of terminals have been clarified
- Table A.1 has been completed with symbols specifically for SMD-packages
- Annex B "Standardization philosophy" has been deleted
- A normative Annex with special rules for SMD packages has been added
- The examples of semiconductor device drawings have been aligned to state-of-the-art
- Packages including SMD-packages 
