Take the stressful twist out of your measurements with this fantastic helix draw set this bit of kit extends out to a diameter of 320 millimetres with the capacity to extend a little over an extra 140 millimetres with a fine extension arm for larger piecesfor geometric precision this set is an excellent piece of stationary for you or your kidscontains pen clampadjustable thumb wheelsideal for technical drawinghelix draw set 6 pack