Made of high quality borosilicate glass 3.3 having very low coefficients of thermal expansion for resistance to heat, and a very high resistance to chemical attack. Annealed at 800 degree Celsius ,can be heated directly in an open flame and can with stand typical laboratory thermal variations in Chemistry processes like heating and cooling. US Standard Size Joint Will Fit into European Standard Size Joint: Standard Taper Ground Glass Joints are interchangeable. For either frosted, presicon-ground standard taper joints (same size),the inner ground surfaces (male joint) make a good seal with the outer(female joint)). The joint size is described by the form A/B. The first number A represents the outer diameter (OD) in millimeters (mm) at the widest point of the inner (male) joint and the second number B represents the length of the joint. For example, a 14/20 joint is 14 mm wide at the top (the widest part) and is 20 mm in length. The joint has a standard taper 1:10, any two joints (male and female) with the same outside diameter (A)can fit into each other ,no matter how length the joints are. For example, a 24/40 (US standard size) joint on a condenser will fit into a 24/29 (European standard size)flask but the ground glass joint will protrude (40 - 29) 11mm into the flask.