103 



NOTES AND CORRESPONDENCE. 



On the Universal Screw — The remarks of Mr. Brooke, ap- 

 pended to my paper on the universal screw, which was pub- 

 lished in a previous number of the ' Journal/ are so entirely at 

 variance with my own experience, that I venture to give 

 somewhat of an answer to each of his paragraphs, excepting 

 the first, which is merely introductory. 



In the first place, then, no workman, be he ever so 

 " practised," can cut up a screw-tool by hand, that, as an 

 exact counterpart of the " hob/' shall be equal to one made 

 by a screw-cutting lathe ; and there are plenty of shops in 

 London and other places where screw-tools can be properly 

 cut up, by comparatively inexperienced workmen. 



" The practical difficulties" next mentioned by Mr. Brooke 

 are entirely illusive. If the method of gauging the tops of 

 the threads were sufficient, nothing would be easier than to 

 make both inside and outside screAvs fit easily and pleasantly 

 in the gauges, and they would screw together in a similar 

 manner; the variations which really occur in the screws 

 made by different makers, to cylindrical gauges of the same 

 size, are at the bottom and sides of the threads. 



Mr. Brooke, in the next paragraph, states, that " the 

 bottom of the outside screw can be most easily gauged/ 5 

 but I am convinced that he cannot have tried it ; for he goes 

 on to say, that if screws u enter easily and pleasantly," they 

 must " necessarily" differ in size some " two or three thou- 

 sandths of an inch," whereas Mr. Whitworth has shown that 

 a variation of one ten-thousandth of an inch is most dis- 

 tinctly perceptible. 



The reason why the adjustible screw-cutting gauge pos- 

 sesses an " immunity from the same wear as that to which 

 the screw-tool is liable," is because it has so very little to do. 

 The screw-tool cuts up the whole depth of the thread, the 

 cutting-gauge only removes that which is left by the wear of 

 the screw-tool. 



I think many persons will find it difficult to understand 

 Mr. Brookes's next paragraph, and the only explanation I 



