312 



KEPOET 1882. 



fully, tabulated their several dimensions, and plotted the results by the 

 ordinary method of linear co-ordinates. They determined the mathe- 

 matical equations to curves that most closely corresponded with the 

 ratios of diameter to pitch thus found to have been employed in practice, 

 and adopted the one which most nearly represented the mean average 

 proportions of the screws in use at various shops and in different countries. 



The Swiss Committee took 1 millimetre pitch as the basis of their 

 system. It was agreed that such a pitch was best adapted to a screw 

 having a diameter of 6 millimetres. The form of thread adopted was 

 triangular, the angle made by producing the two sides being approximately 

 47^°; the depth being i of the pitch, the top being rounded off bj- a 

 radius -Jr and the bottom by a radius J of the pitch. 



The Committee has had an opportunity of examining screw- plates and 

 numerous packets of the corresponding screws manufactured on this 

 system. 



The following table gives the pitches and diameters in millimetres 

 and ' mils ' ' to two significant figures, and the number of threads per inch 

 of all the screws comprised in the small screw series, which happens to 

 cover the exact ground to which the attention of the Committee has been 

 specially directed, namely, diameters below the ^-inch. 



Table of S}viss Screws. 



The ' mil ' is the thousandth i^art of the British inch. 



