This feature as a simple cell property is planned for the future updates of iGrid. To implement it in the current version, you should use the TextBoxFilterChar event which is the universal event to control cell text input.
Here is a C# example from the help which demonstrates how to limit the entered text by 5 characters:
private void iGrid1_TextBoxFilterChar(object sender, iGTextBoxFilterCharEventArgs e)
{
if (iGrid1.TextBox.Text.Length == 5)
e.Char = (char)0;
}
If you need this only for some columns, test e.ColIndex before suppressing the char input with the help of 'e.Char = (char)0' statement.