Rack rails - standards?
pete at dunnington.plus.com
Sat Mar 17 11:48:49 CDT 2007
Mr Ian Primus wrote:
> So, basically, is there a standard for these things
> at all? Any hole spacing or rail size standard, or did
> every manufacurere just make their own?
ANSI/EIA-310-D-1992 or ISO/IEC 60297 (not 60927 as listed in innumerable
Sun documents!) are current, but the standard goes back decades.
The standard defines the spacing between left and right front rails
(17.75"), between the hole centres on the left and right rails (18.25"),
and vertically between the holes (see below). The 19" designation you
often see is the width of the front panel that bolts onto the rails.
The distance from front rail to back rail isn't standardised and in
practice that does vary widely between racks, in fact some racks only
have rails at the front. We have racks that are 600mm deep, 650mm,
850mm, and 950mm, and with the front rails set back various different
distances from the front door (on racks that actually have a front door).
American racks often have round holes (I've seen Sun, DEC and SGI racks
like this) and use Tinnerman nuts, usually 10-32 UNF thread, which is
very similar to European M5 thread. European racks tend to have square
holes to put cage nuts into; these are usually M6 thread/size but
sometimes M5. On racks with round holes, sometimes a small plate with 3
or 4 tapped holes to match four holes in the rack is used instead of
To see a Tinnerman nut, look at the the picture of a Palnut at
there's a thin hexagonal nut welded onto the back instead of the simple
formed thread shown there) and another common style is shown in the
diagram 1/4 of the way down
For a cage nut see
However all the racks and frames I've seen, US or European, have the
same vertical hole spacing to ANSI/EIA-310-D-1992, not the same spacing
between every hole but repeated in "units" of three holes -- hence the
"42U" designation you sometimes see for a six-foot rack. 1U is 1.75",
and the distance between centres of the middle hole and the upper and
lower holes are 5/8", and that means the distance between centres
between the lower hole of one U and the upper hole of the next U down,
is 1/2". There's sometimes a mark -- a scribed line or a small notch in
the rail edge -- between one U and the next.
Pete Peter Turnbull
University of York
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