can I set false to the column size

when i created one grid. my problem is when i drag the columns in the header it changed the column size. how i can set false to entire column size. that will be constant.it can not be change

Disable resizing for all columns -

obj.getSeparatorTemplate().setStyle("cursor", "default");
obj.getSeparatorTemplate().setEvent("onmousedown", "");

Single column (first) -
obj.getSeparatorTemplate(0).setStyle("cursor", "default");
obj.getSeparatorTemplate(0).setEvent("onmousedown", "");