[Principles of making of external telescope crown].

The functioning of telescope crowns consists of pulling on the external crown by telescope principle on the internal crown due to which a friction is caused, which has a decisive role in retention of each telescope restoration. In order to achieve the greatest friction power of each telescope crown, it is indispensable to make every internal telescope crown in a parallelometer and on milling principle. The external crown may be made by applying several laboratory procedures. By analyzing the friction power, it was concluded that the most proper way for making of external telescope was the principle of "doubler" model of refractory material, while the other methods of making gave poor results.