<s>
A	O
600	B-Protocol
series	I-Protocol
connector	I-Protocol
is	O
an	O
obsolete	O
three-pin	O
connector	O
with	O
up	O
to	O
six	O
conductors	O
.	O
</s>
<s>
It	O
was	O
for	O
many	O
years	O
the	O
standard	O
telephone	O
service	O
connector	O
in	O
Australia	O
,	O
but	O
has	O
now	O
been	O
replaced	O
by	O
the	O
six	O
position	O
modular	B-Architecture
connector	I-Architecture
in	O
this	O
application	O
.	O
</s>
<s>
The	O
non-conducting	O
spigot	O
of	O
the	O
original	O
605	B-Protocol
plug	I-Protocol
was	O
provided	O
with	O
a	O
hole	O
for	O
a	O
countersunk	O
screw	O
,	O
allowing	O
the	O
plug	O
to	O
be	O
fixed	O
in	O
a	O
wall-mounted	O
socket	O
.	O
</s>
<s>
The	O
original	O
610	B-Protocol
socket	I-Protocol
was	O
provided	O
with	O
two	O
mounting	O
holes	O
,	O
one	O
behind	O
the	O
receptacle	O
for	O
the	O
plug	O
spigot	O
,	O
and	O
both	O
for	O
countersunk	O
screws	O
.	O
</s>
<s>
Similar	O
to	O
610	B-Protocol
,	O
but	O
with	O
the	O
contacts	O
of	O
pairs	O
one	O
and	O
two	O
allowed	O
to	O
connect	O
when	O
no	O
plug	O
is	O
inserted	O
,	O
contact	O
1	O
connecting	O
to	O
2	O
and	O
5	O
to	O
6	O
.	O
</s>
<s>
This	O
function	O
is	O
not	O
generally	O
supported	O
by	O
modular	B-Architecture
connectors	I-Architecture
.	O
</s>
<s>
Modular	B-Architecture
connectors	I-Architecture
providing	O
suitable	O
switch	O
contacts	O
are	O
available	O
but	O
not	O
common	O
;	O
Instead	O
,	O
mode	O
3	O
devices	O
use	O
two	O
modular	B-Architecture
connectors	I-Architecture
,	O
one	O
for	O
the	O
incoming	O
line	O
and	O
the	O
other	O
for	O
the	O
outgoing	O
line	O
.	O
</s>
<s>
The	O
convenience	O
of	O
using	O
a	O
single	O
connector	O
in	O
this	O
application	O
is	O
one	O
reason	O
for	O
the	O
continued	O
use	O
of	O
600	B-Protocol
series	I-Protocol
connectors	I-Protocol
,	O
but	O
mixing	O
this	O
wiring	O
scheme	O
with	O
modular	B-Architecture
connectors	I-Architecture
does	O
not	O
work	O
well	O
.	O
</s>
<s>
Many	O
recent	O
611	B-Protocol
sockets	I-Protocol
have	O
a	O
stepped	O
recess	O
for	O
the	O
plug	O
spigot	O
,	O
to	O
accept	O
a	O
plug	O
with	O
a	O
larger	O
spigot	O
but	O
still	O
provide	O
a	O
good	O
fit	O
for	O
a	O
standard	O
605	B-Protocol
plug	I-Protocol
.	O
</s>
<s>
Equipment	O
requiring	O
mode	O
3	O
connection	O
can	O
then	O
be	O
equipped	O
with	O
these	O
larger	O
spigot	O
plugs	O
,	O
to	O
prevent	O
this	O
equipment	O
being	O
connected	O
to	O
a	O
610	B-Protocol
socket	I-Protocol
which	O
does	O
not	O
provide	O
mode	O
3	O
support	O
.	O
</s>
<s>
These	O
plugs	O
were	O
also	O
used	O
on	O
Telex	B-Application
machines	O
within	O
Australia	O
.	O
</s>
<s>
Some	O
incorporate	O
an	O
adaptor	O
plug	O
which	O
includes	O
a	O
610	B-Protocol
socket	I-Protocol
,	O
often	O
with	O
all	O
six	O
conductors	O
connected	O
,	O
allowing	O
the	O
extension	O
to	O
also	O
serve	O
as	O
a	O
double	O
adaptor	O
.	O
</s>
<s>
Double	O
adaptors	O
are	O
almost	O
always	O
six	O
conductor	O
,	O
wired	O
pin	O
to	O
pin	O
,	O
with	O
a	O
605	B-Protocol
plug	I-Protocol
and	O
two	O
610	B-Protocol
sockets	I-Protocol
in	O
parallel	O
.	O
</s>
<s>
A	O
mode	O
3	O
adaptor	O
appears	O
physically	O
to	O
be	O
a	O
double	O
adaptor	O
,	O
but	O
the	O
sockets	O
are	O
one	O
610	B-Protocol
and	O
one	O
611	O
,	O
with	O
pair	O
one	O
of	O
the	O
610	B-Protocol
wired	O
to	O
pair	O
two	O
of	O
the	O
611	O
,	O
and	O
pair	O
one	O
of	O
the	O
611	O
to	O
pair	O
one	O
of	O
the	O
plug	O
.	O
</s>
<s>
Adaptors	O
to	O
modular	B-Architecture
connectors	I-Architecture
may	O
connect	O
only	O
pair	O
one	O
,	O
or	O
pairs	O
one	O
and	O
two	O
,	O
or	O
all	O
six	O
conductors	O
.	O
</s>
<s>
Modems	O
and	O
other	O
equipment	O
supplied	O
in	O
Australia	O
are	O
nowadays	O
normally	O
provided	O
with	O
a	O
modular	B-Architecture
plug	I-Architecture
,	O
and	O
an	O
adaptor	O
which	O
connects	O
only	O
pair	O
one	O
,	O
allowing	O
the	O
modular	B-Architecture
plug	I-Architecture
to	O
be	O
used	O
with	O
a	O
610	B-Protocol
or	O
611	B-Protocol
socket	I-Protocol
in	O
need	O
.	O
</s>
<s>
When	O
phones	O
moved	O
to	O
electronic	O
ringers	O
and	O
tone	O
dialling	O
,	O
the	O
additional	O
socket	O
wiring	O
using	O
pins	O
3	O
and	O
5	O
was	O
no	O
longer	O
needed	O
for	O
suppression	O
and	O
the	O
use	O
of	O
only	O
pair	O
one	O
,	O
with	O
white	O
on	O
pin	O
2	O
and	O
blue	O
on	O
pin	O
6	O
became	O
the	O
standard	O
socket	O
wiring	O
,	O
until	O
being	O
superseded	O
by	O
the	O
modular	B-Architecture
connector	I-Architecture
.	O
</s>
<s>
All	O
connection	O
schemes	O
connect	O
pair	O
one	O
to	O
the	O
centre	O
two	O
connectors	O
on	O
the	O
modular	B-Architecture
connector	I-Architecture
.	O
</s>
<s>
Even	O
if	O
no	O
modular	B-Architecture
connector	I-Architecture
is	O
included	O
in	O
an	O
extension	O
cable	O
,	O
most	O
600	O
series	O
extension	O
cables	O
are	O
four	O
conductor	O
.	O
</s>
