438 



REPORT — 1900. 



a screw machine tends to produce rounded threads, and the natural course 

 of trade conditions tends to the reproduction of current forma, the common 

 use in Switzerland of screws with rounded threads does not necessarily 

 show that such a form has especial merit, or had originally been delibe- 

 rately designed. It may be only the result of working conditions. 

 Professor Thury, in defining his thi'ead, chose a form which could be easily 

 produced with fair accuracy, is perfectly etlicienc, and can be conformed 



Fig. 1. 



to in practice, but we venture to think it fails to meet other important 

 conditions 



To ascertain the conditions which should determine the form of a 

 screw thread, consider the mode of action of a screw holding two pieces 

 together. In fig. 1 the screw serves to hold the plate a to the solid 

 part u, and a small part of the thread is drawn on a larger scale below. 

 The action of the screw depends on the tensile strain due to the pressure 



