TYPES OF STOPCOCK Pinch clip burettes are an older and simpler design mainly used in education. Glass key stopcocks are the traditional type and are preferred by some teachers and technicians because of the smooth action, greater control and longer life than PTFE key stopcocks. These usually require light lubrication, using Silicone grease. PTFE key stopcocks are now the most frequently used because they do not need any lubrication, are less likely to jam than glass stopcocks, and are regarded as a lower maintenance option. Modular PTFE key stopcocks are made entirely of PTFE and are particularly suitable for schools as they are less delicate than the other types and all of the parts are replaceable separately. ‘Rotaflo’ type burettes have a screw in/out PTFE key which allows for fine drop control. TYPES OF GRADUATIONS Different colour graduations can be useful, depending on the colour of the solution being titrated. Blue graduations - good for general purpose use. White graduations - useful when using dark coloured solutions. Black or amber graduations - useful when using light coloured or clear solutions.