OX A GAUGE FOE SMAEL SCREWS. 2Si 



Second Report of the Committee, consisting of Sir Joseph Whit- 

 worth, Sir W. Thomson, Sir F. J. Bramwell, Mr. A. Stroh, Mr. 

 Beck, Mr. W. H. Peeece, Mr. E. Crompton, Mr. E. Rigg 

 {Secretary), Mr. A. Le Neve Foster, Mr. Latimer Clark, Mr. 

 H. Trueman Wood, and Mr. Buckney, appointed for the purpose 

 of determining a Gauge for the manufacture of the various small 

 Screws used in Telegraphic and Electrical Apparatus, in Clock- 

 work, and for other analogous purposes.* 



1. Since the presentation of its first Report on a gauge for small 

 screws at the meeting of the Association held in 1882 at Southampton, 

 this Committee has further examined into the recommendations there 

 made, with the result that they now have to propose some important 

 modifications, the general effect of which will, it is felt, be to materially 

 facilitate the introduction of the system. 



2. The want of unanimity on the part of the Committee referred to 

 in paragraph 7 of that Report arose mainly on the question as to whether 

 the inch or millimetre should be taken as a unit of measurement. It is 

 evident that if either is rigidly adhered to, and in any way employed 

 in the nomenclature of the screws, as, for example, in specifying the 

 diameter, pitch, or threads per inch or per mm., the same dimensions 

 could not be expressed in whole numbers in the other unit, and thus a 

 material obstacle would be at once introduced to its general adoption. 



3. It should be pointed out, however, that it has hitherto been the 

 common practice to designate such small screws as the Committee alone 

 is considering, not by any specific dimension, but by a number, which as 

 a rule is arbitrarily chosen and does not of itself form a guide to the 

 size of the screw. Considering, then, that the unit of measurement is 

 only indirectly connected with the subject of a screw gauge, the Com- 

 mittee has felt that the two units might be reconciled so far as relates 

 to such a subject, and that thus one important difficulty would be 

 removed. 



4. The manner in which the series of screws adopted lately by Swiss 

 manufacturers is correlated has been sufficiently explained in the 

 previous Report, and very full explanations are given in the two original 

 pamphlets to which reference is there made. 2 The diameter (D) is 

 related to the pitch (P) by the formula D = 6 Pf, (1), all measure- 

 ments being in millimetres, and P having successively the values 

 1 (or 09°) mm.; 09 1 mm. ; 09 2 mm.; 0'9 3 mm. . . . 0-9" mm. 



Thus ii, the index, becomes a convenient designating number for the 

 screw, and the formula (1) may be expressed D = 6 (0'9 n )£, where 

 P=09". 



■j. The pitch of any screw can be at once ascertained from its desig- 

 nating number by raising 09 to the power indicated by that number; and 

 from this pitch the diameter is directly deducible by the formula (1), so that 

 the number (n) given in the first column of the table, by which a screw 

 is known, is intimately related to all its dimensions. 



P , ee ^P 01 * °f- tne Council presented to the General Committee at Montreal. 

 - Syttematiqite des vis Horlor/cres, by Prof. M. Thury, Geneva, 1878. Notice svr le 

 Systhme des vis de la, Filicrc Suisse, Geneva, 1S80, by the same author. 



