Draper expert 600mm plumb site dual view 39 i 39 beam girder section level draper expert 41213 b i expert quality i b with front viewing plumb site 174 dual view 153 vial and i beam vial manufactured from hardened aluminium electrostatically powder coated and baked with polyester acrylic paint milled top and base and rubber end caps one horizontal and two vertical vials one of which has a front viewing plumb site 174 dual view 153 vial accuracy 1mm per 1m 0 001 17