4.66 REPORT—1899. 
The American, or flav-ended, form of thread appears to be rapidly 
establishing itself in France and Germany, judging from the reports we 
have received of the French and Zurich Conferences, and we understand 
that it is entirely employed by the French Admiralty and by several of 
the French railway companies. These reports refer, it is true, to screws 
of larger sizes than are included in the range of the British Association 
and Professor Thury’s systems. The conclusions of the recent Conference 
at Zurich, which adopted the flat-ended thread, were expressly limited to 
screws of more than 6 mm. diameter, the extreme upper limit of our 
system. Buv so far as the easy production of accurate form is concerned, 
arguments which apply to large screws apply with greater force to small 
serews ; while a form which is suitable for all screws above 6 mm. cannot 
be wholly unsuitable for screws below that limit. The Committee, more- 
over, were informed by one of their number that he has used screws of the 
American form in sizes corresponding with some of the smaller numbers 
of the British Association series, and has found them perfectly satis- 
factory. 
Current conceptions of the possible and desirable limits of aceuracy in 
mechanical construction are rapidly advancing, and while we recognise 
the value of the work of the Committee of 18S2 in establishing a generally 
accepted thread, we are dissatisfied with a standard form for a piece so 
important as a screw which is open to the serious objection referred to 
above. 
We recommend that this Committee shall be reappointed for the pur- 
pose of considering whether the British Association form of thread for 
small screws should be modified. 
APPENDIX.—ReEports oN SCREWS MADE BY THE PRATT AND 
WHITNEY ComMPANny. 
I.— Report by CotoneL Warkin, &.A., C.B. 
The Wilderness, Woolwich: July 11, 1899. 
The Secretary British Association. Screw Gauge Committee. 
T have now taken photographs of the screws sent by the Pratt and 
Whitney Company for the Committee, prints of which I enclose. 
I find the general forms of these screws are better than those we kave 
obtained heretofore, which is satisfactory, taking into consideration the 
fact that they are constructed of hard steel. 
As in former cases, the larger sizes conform more nearly to the British 
Association pattern thread, the rounding in the smaller sizes being not 
quite so satisfactory. 
The angle of the thread in the two large sizes is about 49°, but con- 
siderably more in the No. 13 size. 
As regards linear dimensions, all the screws are nearly perfect, as will 
be seen by the measurements given on the back of the photographs. 
The diagonal scale accompanying the photographs was constructed 
from the scale photographed at the same time as the screws. 
The gauges may, I think, be accepted as sufficiently correct for all 
practical purposes as standard gauges for British Association pattern 
screws. (Signed) W, WarTKIN. 
