<s>
A	O
buckling	B-Device
spring	I-Device
is	O
a	O
type	O
of	O
keyswitch	B-Device
mechanism	O
,	O
popularized	O
by	O
IBM	O
's	O
keyboards	B-Device
for	O
the	O
PC	B-Device
,	O
PC/AT	O
,	O
5250/3270	O
terminals	O
,	O
PS/2	O
,	O
and	O
other	O
systems	O
.	O
</s>
<s>
It	O
was	O
used	O
by	O
IBM	O
's	O
Model	B-Device
F	I-Device
keyboards	I-Device
(	O
for	O
instance	O
the	O
AT	B-Device
keyboard	I-Device
)	O
,	O
and	O
the	O
more	O
common	O
Model	B-Device
M	I-Device
.	O
It	O
is	O
described	O
in	O
(	O
Model	O
F	O
)	O
and	O
(	O
Model	B-Device
M	I-Device
)	O
,	O
both	O
now	O
expired	O
.	O
</s>
<s>
The	O
coil	O
spring	O
tensed	O
between	O
the	O
keycap	B-Device
and	O
a	O
pivoting	O
hammer	O
buckles	O
(	O
i.e.	O
</s>
<s>
kinks	O
or	O
collapses	O
)	O
at	O
a	O
certain	O
point	O
in	O
its	O
downward	O
traverse	O
,	O
providing	O
auditory	O
and	O
tactile	O
feedback	O
to	O
the	O
keyboard	B-Device
operator	O
.	O
</s>
<s>
In	O
a	O
Model	B-Device
M	I-Device
,	O
the	O
electrical	O
contact	O
is	O
a	O
membrane	O
sheet	O
similar	O
to	O
that	O
of	O
a	O
modern	O
dome	O
switch	O
keyboard	B-Device
.	O
</s>
