386 BEPORT— 1903. 



that machine-made sctews will enter the nuts or tapped holes. The out- 

 line of this is A B E G L O Q T U. 



D. A notch gauge to test the core diameters of male screws. 



E. A hole limit gauge to test crest diameters of male screws and to be 

 checked by piece A. The diameter of this is diameter D, fig. 1, 

 Schedule I. 



F. A cylinder plug gauge to test the diameter of the hole in the gauge 

 nut C in commercial nuts or tapped holes. 



The diameter of this is diameter C, tig. 1, Schedule I. 



2. That the standard B. A. screw be defined as a screw which conforms 

 to the gauges described above in all respects except in the form of the crest 

 and root of the thread, which are unimportant. 



R. E. Crompton. 



J. M. GORHAM. 



G. K. B. Elpiiinstone. 

 Mark Barr. 

 C. Vernon Boys. 

 O. P. Clements. 

 W. A. Price. 



APPENDIX, 



The Committee have had constructed for them by the Cambridge 

 Scientitic Instrument Company a machine for measuring small screws 

 microscopically. In figs. 4 and 5 ar(; given drawings of the instrument, of 

 which fig. 4 is a plan of the compound stage with the microscope removed, 

 and fig. 5 is an end elevation showing the arrangement of tlie microscope. 

 The screw to be measured is held in a spring chuck in the spindle (A). 

 By means of the two micrometer screws, S, S.^, the screw is moved along 

 geometric slides in two directions at right angles. The screw is aligned 

 parallel to the micrometer S, by the adjusting screws B C. The pitch of 

 the micrometer screws (which were supplied by the Browne and Sharpe 

 Company) is 0-5 mm., and the heads are divided into fifty parts, enabling 

 readings to be taken directly to 0-01 mm. 



The screw is illuminated from below by a plane mirror and is observed 

 by the microscope M. Hough focussing is effected by sliding the micro- 

 scope in the tube T, the tine adjustment being accomplished by the 

 micrometer screw S;,, which raises and lowers T. The tube T can also be 

 rotated about its axis without disturbing the focus, and the amount of 

 rotation measured by means of a scale on D. The eyepiece and object- 

 glass of the microscope are by Zeiss. The eyepiece is furnished with 

 suitable crcs«-wires in silver. 



A series of spring chucks for different diameters of screws accom- 

 panied the machine. 



