This parameter holds the Radius of the currently selected tool.
The field can be edited if you wish to temporarily change the value of the currently selected tool. Changing this field does not change the value of the tool in the tool list! It is for temporary editing only. This value will determine the tool path offset distance from the geometry.
If you are using the Tool Path Verification software (MCU), this will change the tool size as well as changing the offset amount of the toolpath resulting in a completely inaccurate back plot.
You should instead use the Offset Dim in the cycle information to change the amount of the tool offset.
When setting the tool radius, it is important to remember that this is used as the offset for the tool path and if you are using a shaper cutter, the radius may not be half of the diameter.
Look at the following images:
Radius is half of smalles diameter
Radius is half of smallest diameter
In both of these cases you would only want to offset the tool path by half of the smallest diameter. However for lead-in and lead-out clearance, the diameter is the largest diameter so that you account for the entire size of the tool in the tool path. In this case the radius is not half of the diamter.