---
title: T (Tool number)
slug: t-tool-number
docTags: 
createdAt: 2023-04-19T10:21:43.000Z
---

The T parameter in G-code is a value that represents the tool selection or tool change command, which is used to specify the machine's tool or device being employed for a particular operation. This parameter can be applied to various machines and processes, such as milling, turning, or laser cutting, where multiple tools or devices may be used within a single program. The T parameter is typically followed by a tool number, which corresponds to a specific tool in the machine's tool library or carousel. It plays a significant role in managing the sequence of operations and ensuring that the correct tool is engaged for each process in a multi-tool machining setup.

To select a tool, program `T...`, where the number is the tool changer slot for the tool. The tool is not changed until an [M6 (Tool Change)](docId\:kQG7dD1dpwUw3hchbArUT) command is programmed. The T-word may appear on the same line as the `M6` command or on a previous line. 

It is possible to program a T word more than once before a tool change takes place, but only the last issued statement is taken into consideration. The carousel may move a lot, but only the most recent T-word will take effect at the next tool change. It is OK to 

It is possible to issue `T0` this means that no tool will be selected. This is useful if the spindle needs to be empty after a tool change. 

An error occurs if: 
•	a negative T number is used, 
•	a T number larger than the number of slots in the tool changer is used.