266 BELL SYSTEM TECHNICAL JOURNAL 



placed on this wire, the main feature of concern being brittleness. 

 The elongation measured in an 8 in. length must be between 1 and 

 4 per cent for wire up to and including No. 27 gage and 1| to 7 per 

 cent for No. 28 gage wire and heavier. The wire is also subject to a 

 kinking test in which No. 30 wire and smaller shall kink without 

 breaking. This last test indirectly controls the tensile properties of 

 the wire. 



Summary 



A review has been given of the more common types of telephone 

 apparatus springs. Vast quantities of these springs are employed in 

 the telephone plant and the numerous factors that must be considered 

 with regard to selecting material have been reviewed. The materials 

 most generally used have abundant competitive sources of supply 

 and the quality is carefully controlled by tests that are designed to 

 be easy to apply and effective in evaluating the properties desired. 



