382 



REPORT — 1903. 



Schedule IV. — Schedule of maximum and minimtim diameters of the cores of 

 screws, and of the outside diameters of taps, where clearance is provided. 



If clearances up to the amount indicated in Schedule IV. be generally 

 adopted by makers, interchangeability will, in the opinion of the Com- 

 mittee, be thereby promoted ; and the Committee recommend that, except 

 in the case of screws made for special cases, the above clearances in the 

 core and outside diameters of the screws be adopted as normal. 



As appears from the above considerations, for many purposes the 

 Committee do not attach great importance to the exact form of the thread 

 at the crest and root. 



While adhering then to the form of the thread as laid down in the 

 Montreal Report, and in Schedule I. above, they would advise tlie accept- 

 ance as B.A. screws of all screws which pass the nut gauge (1) described 

 below and have the requisite core and outside diameters, and of wliich 

 the straight portions of the sides are not less than those of the standard 

 screw. 



The Committee have given a very long time to the consideration of 

 various forms of gauges. As appears from their earlier reports, it is clear 

 that the difficulty of constructing gauges witli rounded crests and roots 

 has not been overcome, and the Committee are reluctantly compelled to 

 relinquish the task of making gauges of the ideal B.A. form following 

 the outline A, B, c, D, E, f, g, n, k (fig. 2). Two possible forms of flat-topped 

 gauges for screws have been considered : (1) a gauge following the outline 

 A, c, N, 0, G, K ; (2) a gauge following the outline A, L, M, N, o, p, q, k. 

 With regard to (1) it is clear that while It will test the pitch and the 



