Bent vials start out as a straight glass tube which is heated and then formed into a radius. The principal of operation is that the bubble will move to the highest point of the radius as gravity acts on the liquid inside the vial. This is explained in more detail on our page explaining sensitivity. The radius can vary from 50mm to 5000mm in order to produce vials with a range of sensitivity from 2.3degrees to 2' (minutes). There are physical limitations to what will work effectively as a vial relating to the diameter, the sensitivity, the bubble size and the choice of liquid. If the glass diameter or the bubble is too small then the bubble may stick in position. If the vial is too large and the bubble is too small, then there will be a restricted upper temperature limit. These are all things we have much experience of, and as such can advise you, or design a vial to meet your exact requirements. We also offer Tritium illuminated levels (also known as Betalights or Trasers) which require no power supply, have a life of up to 20 years and enable the bubble position to be clearly visible in the dark. Please contact us for more details.