Glossary Updates12 new terms added to the glossaries · October 2, 2026, 22:44 CEST
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Glossary · CNC and machine tools

Block number

Also known as: Sequence number, N number

German: Satznummer

In CNC programming, a block number is the optional sequence number at the start of a program block, written with the address letter N, that identifies the block within an NC program.

  • CNC
  • Standards

In one sentence

A block number (N word) labels a block in an NC program so operators and programs can refer to it; it does not change the execution order.

Example

The line N0120 G01 X50.0 F200 carries the block number 120, which the operator uses to restart the program after a tool change.

How it applies

  • Programming: Block numbers are usually written in steps of 5 or 10 so blocks can be inserted later without renumbering. Most controls execute blocks in the order they appear in the file, not in the order of their numbers.
  • Operation: Operators use block numbers to search for a restart point after an interruption, a tool break or a program stop, depending on the functions the control offers.
  • Documentation: Setup sheets and work instructions that refer to specific blocks (for example 'check the dimension after N0340') must be updated whenever the NC program is revised. Treat the program revision and the referring document as one change under Configuration control.

Block number vs. program block

The Program block (NC) is the complete line of instructions: preparatory functions, coordinates, feed rate and miscellaneous functions. The block number is only its label. A block without a number is still a valid block on most controls.

By knowledge.aitechdoc.world · Published September 26, 2026 · Last reviewed

Source: ISO 6983-1:2009, Automation systems and integration — Numerical control of machines — Program format and definitions of address words — Part 1: Data format for positioning, line motion and contouring control systems

Definitions follow the cited standards and specifications. Where a source is a copyrighted publication, such as an ISO, IEC or EN standard, the definition is a close paraphrase, not a verbatim quotation, so as not to infringe copyright. We recommend reading the original publication. The sections “How it applies” are editorial commentary by AI TechDoc Blog and are not part of any standard.

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