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{dataIndex: 'nit_1', header: 'Cedula', align: 'right', xtype: 'numbercolumn', format:'0,000', width: 110,},

// or with letters

{dataIndex: 'nit_1', header: 'Cédula', align: 'right', width: 110, renderer:v=>!isNaN(v)?Ext.util.Format.number(v, '0,000.##'):v,},