ON THE SMALL SCREW GAUGE. 



383 



effective diameter, it will not gauge the root of -the thread, and will not 

 therefore separate screws which are interchangeable with a standard nut 

 from those which are not. Besides testing a screw with a nut gauge of 

 this form, it will be necessary to test its core diameter by means of a gap 

 or notch gauge. If the screw pass the nut gauge, and have at its root the 

 clearance recommended, it is practically certain it will be interchangeable 

 with a nut of standard form. A screw which passes this gauge and 

 has the requisite diameters as given in Tables I. and II. at the core 

 and outside, and the requisite bearing surface, may be called a B.A. 

 screw. 



Tlie other form of flat-topped gauge which has been considered follows 

 the outline A, l, m, n, o, p, q, k. A gauge of this form will test the mini- 

 mum diameter, as well as the pitch and effective diameter of screws, and 

 all screws which pass it are interchangeable with the standard nut. 

 Moreover, in view of the clearance recommended at the root, the Com- 

 mittee anticipate that in practice this gauge could be usefully employed. 

 At the same time it is clear that it will not pass a screw any part of 

 which lies above the lines L M, p Q, and that it would therefore reject a 

 screw having the standard form. 



Fig. 2. 



SCREW - 



Thus in conclusion the Committee recommend : 



I. That the form of the standard B.A. thread be that defined at the 

 Montreal meeting in 1884, and which follows the outline A, b, c, n, e, f 

 c, H, K of fig. 2. 



II. That the form of the B.A. gauge for screws be that defined by the 

 outline a, c, n, o, g, k, and that this be used with a gap or notch gauge, as 

 described in the report. 



III. That the dimensions of the notch gauge be such as to ensure that 

 the core diameters lie between the limits given by Schedule IV. 



IV. That a screw which passes the B.A. gauge, and of which the 

 core and outside diameters are given by Table II. and Table I. respec- 

 tively, be accepted as a B.A. screw, provided that the length of the 



