528 REPORT—1896. 
Dimensions in Millimetres Demensipns in Thousandths 
of an inch Threads 
Number _per 
Diameter Pitch Diameter Pitch inch 
I II IIL IV Vv VI 
10 17 0:35. 67 13°8 72°6 
iil 15 0°31 59 12:2 81:9 
12 13 0:28 51 11:0 90°7 
13 1:2 0°25 47 9:8 101:0 
14 1:0 0°23 3 9:1 1100 | 
15 0-90 0°21 35 8:3 121:0 
16 0°79 0:19 3 (G5) 134:0 
17 0:70 O17 282 6:7 149:0 
18 0°62 0715 24 59 169:0 
19 0:54 0-14 21 5:5 181:0 
20 2 0°47 0:12 19 47 2120 
21 0°42 011 17 4:3 231°0 
22 0°37 0-098 | 15 379 259°0 
23 0°33 0:089 | 1S 3°5 285-0 
24 0°29 0-080 | 11 73152 317:0 
25 0:25 0:072 10 2:8 353-0 
The form of thread adopted was triangular, the sides forming an angle 
of 474°, with the top and bottom rounded off to +ths of the pitch, 
The diameter (D) is related to the pitch (P) by the formula 
D=6 PS, all measurements being in willimetres, and P having succes- 
sively the values :— 
1 (or 0:9°) millimetre ; 0-9! millimetre ; 0-9? millimetre ; 0°93 milli- 
metre; ... 0°9" millimetre. The index (7) thus becomes a convenient 
number designating the screw. 
The reasons supporting these recommendations were fully given in the 
Report submitted by the Committee at the Montreal meeting of 1884. 
Experience has justified the adoption of this gauge, which is almost 
universally used by the electrical trade, and is very considerably employed 
by the clock and instrument makers in the United Kingdom. 
It is not proposed to modify it, but there has been great difficulty in 
obtaining accurate gauges. No official system has yet been adopted by 
which manufacturers can compare their gauges with the standards, nor has 
a home been selected to deposit authorised standards for easy reference. 
British Association screws bought to-day from any screw manufacturer 
are not necessarily of the same dimensions as those supplied by the same 
maker a month ago. Screws supplied by different makers vary consider- 
ably from each other. Measuring gauges now existing, both male and 
female, differ largely from one another, and do not give correctly the true 
form of thread specified in the original Report. The essential element of 
the value of screws made to a standard gauge—their interchangeability— 
has thus never been fully realised. 
The British Association, having had their attention called to these 
anomalies at their last meeting (Ipswich, 1895), appointed a committee 
to consider the subject, which has now the pleasure to submit its first 
Report. 
