AUGUST 12, 1915] 

NATURE 
647 

To correct this, and to bring the gauge to the 
proper dimensions, grinding and lapping by 
machines or hand is required. It will thus be 
understood that the whole operation of gauge- 
making is one which requires great skill, and a 
special plant. 
Many of the gauges used in engineering manu- 
factures are made by firms who lay themselves 
out specially for this class of work; in other cases 
the manufacturing firms make their own gauges. 
The latter plan has nothing against it, provided 
that the whole of the parts required in the finished 
products of the firm are made in their own factory. 
This is a point of importance at the present time, 
when most engineering firms have been called 
into the making of munitions. It is clear that 
the produce of any one firm producing certain 
parts must agree, within the prescribed limits of 
accuracy, with that of any other firm making the 
same parts. Hence all must be supplied with 
gauges having like limits of accuracy. 
TABLE FOR B.A. THREADS. 

the standardisation of dimensions in a similar way 
to that in which are maintained our standards of 
weights used in distributive trades. 
The National Physical Laboratory has recently 
been carrying out a useful piece of work in deter- 
mining the desirable manufacturing limits for 
B.A. screws. Gauges for testing screws present 
peculiar difficulties in manufacture, as will be 
realised from what has been said above. The 
“fit” of a screw having a V thread in a tapped 
hole depends chiefly upon the effective diameter of 
the threads (i.e., the diameter measured between 
the sloping sides of the thread), on the pitch, and 
on the correctness of the angle of the V. The 
National Physical Laboratory has issued tables 
giving recommendations(some of them provisional) 
for BLA: threads, Nos. oi) 1,;2; 3, 45) (5) 6:5 the 
scope and importance of the recommendations 
may be understood by examination of the accom- 
panying table, which we have abstracted from a 
number of tables in the report. 
No. o. 
' All dimensions are in millimetres. 












Finished parts Tools Gauges 
| [eek | | 
F Standard | ' Limits for eee = . . F 
|ys ae Raia Limits for | Screwed Go in Not goin| Goin |Notgoin 
| Li f d | Li for| Li fi 3 x 
[seers lotsaped |eaps |e ies | GAPE | wise | rte | pine” nine. | mes 
| 
: : f 59933 | 6°067 | 6.133 | 6°033 | G6'000 || 5°993 5°933 
Full diameter ... 6°000 l\ 6-a00 | 6-200 || 6-167 6067 6:033 || 6-000 Goce 
| 
eattract 32 eal leas f 5267) 57467 || 5°433 | 5:333 | 5°267 || 5°380 
Effective diameter ... | 5 "400 L833 5.533 5-467 5367 5:300 | 5387 
B00 |f 4°00 | 4800 |} 4°733 | 4°633 | 4°567 || 4:767 | 4800 
ee ae 4800 1) 4-733 4867 | 4°767 | 4667 | 4%00 | 4:73 4°867 
Pitch, over 10 threads 10000 { me aoe Peale eo eso ja eee 
| | | | 
2 f 42h | 423° 45% | 454° 454° || 464" 
Angle of V 474 \ 522° 523° 498° 49% 494° 48° 
| i} 

It is well known, as has been pointed out by a 
correspondent in the Morning Post, that the firms 
of gauge-makers have not been able to keep pace 
with the demand, and that many firms have been 
hindered in the starting of the manufacture of 
munitions by delay in the supplying of gauges. 
It is very easy to say now that the emergency 
might have been foreseen earlier. A very useful 
suggestion was made at a recent meeting of the 
Institution of Mechanical Engineers to the effect 
that all gauges should be made and supplied from 
a central factory. It may not be altogether a 
dream to imagine such a factory under direct 
government control, as is the case in Wool- 
wich Arsenal, and working in conjunction with 
the National Physical Laboratory in order that 
standards may be maintained. Such an institu- 
tion would be of great benefit to engineering 
manufacture, quite apart from the present war 
conditions, and could be worked so as to secure 
NO. 2389, VOL. 95] 
| “not 
| gauge; (f) a “not go in”’ 
The gauges recommended are (a) a screwed 
plug gauge; (b) a screwed ring gauge; (c) a plain 
cylindrical “go in” gauge; (d) a plain cylindrical 
zo, in?, gauges) (e)/eal Seon ine ning: 
ring gauge. Gauge 
(b) would be specified to have the same thread 
form as the plug gauge (a) and would be 
checked by its fit upon the latter. Gauge (c) is 
of standard nominal core diameter, and should 
| fit in gauge (b); gauges (c) and (d) serve the pur- 
pose of testing the core diameters of units and 
tapped holes. Gauges (e) and (f) are for testing 
the full diameters of screws. 
The results of the investigation are bound to be 
of service at the present juncture to instrument 
makers and others using B.A. threads. The 
National Physical Laboratory is prepared, pend- 
ing an authoritative decision on the matter, to 
certify screws, etc., which fall within the sug- 
gested limits, as B.A. screws, taps, or gauges. 
