VESA is an acronym for Video Electronics Standards Association. The current documentation can be purchased through the VESA organization.

Overview

Monitor and Video Display manufacturers produce their products to meet an industry standard which allows compatibility between various products and accessories. This means that if one manufacturer makes the display and a different manufacturer makes a ceiling mount then the two products will fit together without issue.

Mounting Hole Specification Based on Monitor Size

There are several different hole patterns that the VESA standard covers. The following table provides the more common dimensions.

More VESA Information

• Ergo In Demand has a great site for looking up VESA mounting hole patterns for every display made. They also sell great monitor, LCD, and Plasma mounts.
• Video Electronics Standards Association (VESA) website.
• Wikipedia page on VESA

The hole types for racks have changed over time and varies from manufacturer to manufacturer and from application to application. Rack hole type is referenced in the EIA-310 rack specification. However, there is no one hole type that is considered “standard”. This is an overview of the 19″ rack’s standard hole types and their uses.

Threaded Holes

The original standard for 19″ rack mount holes was a threaded hole. There are a variety of thread types today including 10-32, 12-24 and M6 metric. The rack uprights for a threaded hole rack are thicker than unthreaded racks to ensure the threads did not strip out.

Threaded racks work well with audio equipment and boxes that do not use rails. Most shelves are compatible with threaded racks. Most modern OEM server manufacturers only have limited success installing their rails in threaded racks. Third party rails are often required to mount the server in a threaded rack.

Round Unthreaded Holes

IBM was the first to widely use unthreaded holes in an OEM rack, and they used that as a standard for many years. Unthreaded, rack holes can be converted to threaded holes with the use of a clip nut. Clip nuts are not as widely used as cage nuts.

Round, unthreaded holes are popular enough that Dell made a rail specifically for this rack type called the Versa Rail. Most modern IBM and HP rails are also compatible with round, unthreaded holes. Round, unthreaded hole racks are no longer readily available since the introduction of the square hole rack.

Square Rack Holes

The square hole measures 3/8″ x 3/8″. Most racks that use square holes have steel uprights that vary from 0.085″ to 0.110″ thick.

Almost all OEM server racks are now made with square holes. Square holes allow the OEMs to design rapidly deployable rails or Rapid Rails that automatically latch into the square holes. Dell, HP and IBM all have their own versions of the Rapid or Quick Rails. These rails greatly reduce installation time.

The second reason why square hole racks are popular is that the square holes can easily be converted to a threaded hole by the installation of a cage nut. These cage nuts snap into the square holes and are available in a variety of threads.

Most server racks have 4 vertical uprights. These uprights (aka Rack Rails or Mounting Posts) have mounting holes on standard EIA spacing and are used to attach equipment.

There are three types of uprights: “L”, “C” and “?” (shown below). For more information on why upright shapes can cause equipment installation problems, read “Why all racks are not created equal“.

Rack screws are used to attach equipment to the vertical uprights of a 19″ rack. Racks do not have a standard thread type. There are three common thread types for rack screws: 10-32, 12-24 and M6. Since the introduction of the square hole rack and Cage Nuts, the exact thread can be selected and changed at will.

10-32 Threads

10-32 threads are historically the original rack screw type. The term 10-32 comes from Unified and American Screw Threads for Bolts, Nuts, and Machine Screws standards published by ANSI B1.1-1974. The number “10″ is simply a size designator with no numerical meaning. The number “32″ refers to 32 threads per inch. You can identify a 10-32 screw by measuring the diameter with a ruler at exactly 3/16″ (0.190″).

12-24 Threads

12-24 is now more common than 10-32 in pre-threaded racks. 12-24 fasteners are slightly larger than 10-32 and have courser threads. The term 12-24 comes from Unified and American Screw Threads for Bolts, Nuts, and Machine Screws standards published by ANSI B1.1-1974. The number “12″ is simply a size designator with no numerical meaning. The number “24″ refers to 24 threads per inch. You can identify a 12-24 screw by measuring the diameter with a ruler at slightly less than 7/32″ (slightly larger than 3/16″ or 0.210″).

M6 Threads

M6 refers to a metric 6mm screw. The outside diameter of the threads is 6mm. The standard metric rack screw is actually an M6 x 0.1mm. The number “0.1mm” refers to 0.1 threads per millimeter. M6 screws are commonly used by HP. You can identify an M6 screw by measuring the diameter with a ruler at slightly more than 7/32″ (0.228″).

Related Subjects

• 19″ Racks
• Rack Hole Types

Rack mount depth is a commonly confused term. The term is commonly confused with the overall rack depth including the door. The term is defined as the dimension from the front of the front mounting post to the back of the back mounting post. Due to the fact that many cabinets have adjustable mounting posts, the depth can only be accurately determined by measuring it.

Common Depths

The rack mounting depth has been increasing over the years, along with the overall depth of racks. This is caused by the steady increase of the depths of standard servers made by Dell, HP and IBM. Here are the OEM standards:

• Dell standard depth is 28 7/8″
• HP standard depth is 29 1/8″
• IBM standard depth is 28 1/2″

The depth was commonly 19″ to 24″. This depth is still used for Audio Racks. The most common depth is now approximately 29″ since this is close to all OEM’s.

Measuring 4Post Rack Mount Depth

Measuring 2Post Rack Mount Depth (Upright Depth)

2Post relay rack’s mounting depth is also called the Upright Depth. This most common upright depth is 3″, although 5″ and 6.5″ are also readily available.

EIA stands for the Electronic Industries Association. The current revision is EIA-310-D. The EIA-310 document is available for purchase at the IHS website.

Overview

EIA-310 is a specification for what is often called the “standard rack”. This specification standardizes several important features of 19″ racks, such as the Rack Unit (RU or U), vertical hole spacing, horizontal hole spacing, rack opening and front panel width. The specification also sets tolerances on each of these dimensions.

The EIA-310 specification has been the 19″ racks standard for equipment for 50 years. Despite this, RackSolutions believes that the items that the specification does not cover is the real reason for the industry wide incompatibility we now face. Rack features such as hole type, rack mounting depth, front and rear space, and obstructions between front and rear rails are the cause of real rack headaches.

Vertical Hole Spacing

Vertical hole spacing is defined as a repeating pattern of holes within one Rack Unit of 1.75″. The hole spacing alternated at: 1/2″ – 5/8″ – 5/8″ and repeats. The start and stop of the “U” space is in the middle of the 1/2″ spaced holes. See the diagram below.

Horizontal Spacing

The horizontal spacing of the vertical rows of holes is specified by EIA-310 at 18 5/16″ (18.312)(465.1 mm). This dimension is not well maintained on some racks, causing problems with equipment installation. Many manufacturers use equipment mounting slots instead of holes to allow for variations in this dimension.

Rack Opening

The opening in the rack is specified as a minimum of 17.72″ (450mm). 2Post or relay racks tend to have a larger than normal opening, as do many other racks with threaded holes. Square hole racks tend to be very close to the minimum opening.

Front Panel Width

The only dimension on a 19″ rack that actually measures 19″ is the width of the front panel of equipment.

More Information

• What is a 19″ Rack
• What is a Rack Unit (“U” or “RU”)
• Wikipedia has an in-depth overview of 19″ racks.
• Why all racks are not created equal

]]> http://www.server-racks.com/eia-310.html/feed 16 http://www.server-racks.com/big-3.html http://www.server-racks.com/big-3.html#comments Fri, 12 Oct 2007 01:20:13 +0000 bob http://www.server-racks.com/big-3.html Definition

In terms of servers and racks, the Big 3 refers to Dell, HP and IBM. These three OEM’s define the future trends in server form, fit and function. Their advances in terms of racks and rail designs have also changed the landscape of rackmount hardware.

Fixed rails can most easily described as not a sliding rail or telescoping rails. Telescopic sliding rail kits provide the functionality of a drawer, more or less. The server can be pulled out of the rack and serviced without disconnecting all the cables. This functionality is very useful. However, sometimes the slide rails just won’t fit in the rack. In these circumstances, the product that will provide a solution is a fixed rail. A fixed rail is a long L shaped bracket that supports the edge of the equipment. The fixed rail is a catch-all type of product. If nothing else will work, this product will provide the solution. The fixed rail may include a cabling crossbar in the rear to dress out any cables present. The fixed rail requires the servers and equipment to be fully removed from the server rack for service.

Click on photo for a selection of rails

Compatibility

The Big 3 are constantly evolving their sliding rail kits by improving on existing designs. This sometimes prevents slide rail kits from being backwards compatible with previous generation servers and racks. The fixed rail is compatible with most generation servers and equipment.

The hole spacing for standard 19″ racks on the mounting flange is spaced in groups of three holes. This three hole group is defined as a Rack Unit (RU) or sometimes just call a “U”. 1U occupies 1.75″ (44.45 mm) of vertical space. Manufacturers of rackmount equipment make their product lines based upon how many RUs that the equipment occupies in the server rack. The three hole group spacing is measured from center hole to center hole and does not vary, regardless of whether the server rack has square or round mounting holes. This uneven hole spacing can cause installation issues if the installer does not pay close attention to where the slide rail assemblies are being installed. The most common problem is that the slide rail assembly hooks or holes do not line up with the holes in the server rack. This is typically due to the slide rail assemblies being misaligned with the hole pattern or otherwise referred to as “being off a U”.

More Information

• What is a 19″ Rack
• What is EIA-310
• Wikipedia has an in-depth overview of 19″ racks.
• Why all racks are not created equal

The following is a list of the various types of 19″ Racks available:

• Server Racks (aka cabinet racks, equipment racks, 4Post racks)
• Open Frame racks (aka 4post racks)
• 2Post (aka Relay racks, Telco racks)
• Transport racks
• Portable racks
• Wall Mount racks

Server Rack Enclosure

Open Frame Racks

Transportable Racks

2Post Relay Racks