Rack Mount Screws – Small Yet Important Details in Server Rack Design

Tapped holes, round holes, square holes, 10-32, 12-24 and M6 rack mount screws, oh and cage nuts and clip nuts too – there are lots of choices when it comes to fasteners and mounting holes for your rack mounted equipment.  So if you are

10-32 Screws
10-32 Screws

considering which type of mounting hole and hardware you want to use in your new server rack or enclosure, or you have an existing server rack that has hardware or rack mount screws that you haven’t seen before, our short guide to mounting holes and fasteners that follows can be a big help.

Tapped Holes and Screws

In the beginning, all rack mounting holes were tapped to receive a specific type of threaded rack screws.  The three most common sizes of rack screws found in rack mounted equipment are:

  • 10-32 – The “10” refers to the size of the screw and the “32” denotes 32 threads per inch.  It is a very common screw type and is available in different driver styles (Torx and Philips are the most common).
  • 12-24 – Slightly larger than the 10-32, the “12” denotes a thicker screw with thicker, coarser threads (“24” or 24 threads per inch).
  • M6 – Developed in Europe, the M6 measures 6mm at the outside diameter of the thread.  Standards vary, but the most common M6 screw is M6 x 01mm.  HP equipment often calls for M6 screws.

Tapped holes and screw type rack mounts are often used in racks and enclosures where there will be few, if any changes to the equipment configuration.  Good examples are telephony, patch panels, TV broadcasting equipment,studios and Telco Relay racks.  The difficulty with tapped holes and screws is that there is always the possibility that a thread can become damaged, or a screw might bind and break off in the mounting hole.  This will make

Clip Nut
Clip Nut

the mounting hole unusable.  For server racks and enclosures where change is the norm there are other mounting alternatives.

Tools You’ll Need

For installation we recommend an electric screw driver or drill (only if it has an adjustable clutch setting) with the correct Philips, square or star bit.  Use only as much torque at a slow speed to securely fasten the hardware to the rack.

Cage Nut
Cage Nut

Too much torque or speed and the hardware or the tapped holes may be permanently damaged.

Round Holes and Cage Nuts

Initially used by IBM, round holes are unthreaded – the rack mount screws are held in place by cage nuts (most popular) and clip nuts.  A cage nut consists of a spring steel cage that is designed to clip onto the open mounting hole.  Inside the steel cage is a captive nut.  Should a screw become stripped, or break, the nut can be removed and replaced with a new one.    That means the mounting hole itself remains undamaged and usable.  Round holes and cage nuts became so popular that Dell made a rail specifically for them.  However, the most common in unthreaded rack mount holes is the Square Hole.

Tools You’ll Need

Again, we recommend an electric screw driver or drill (only if it has an adjustable clutch setting) with the correct Philips, square or star bit).  Too much torque or speed can still be a problem – but you’ll only end up replacing the cage

12-24 Screws
12-24 Screws

nut and screw (which can be easily removed using one of our cage nut removal tools).

Square Holes, Screw-less Mounting and Cage Nuts

Square holes are the most common now in rack design.  They enable screw-less, tool-less mounting.  With square holes, the rack mount equipment can be hooked down to the lip of the square hole.  This makes it very easy to swap out equipment – so square hole server racks are great for environments where there is a lot of change.  Equipment that is not designed for square hole racks can still be used by simply using cage nuts that will fit in square hole rack rails.

Tools You’ll Need

Types of Rack Mounting Holes
Types of Rack Mounting Holes

None!  That is unless your equipment is not designed for a square hole rack.  Then you’ll need to use the round hole rack installation process.

At Rackmount Solutions we pay attention to details. Our screws and cage or clip nuts are black to blend seamlessly with your rack. We take pride in providing server racks and mounting options to meet every need.  If you’d like more information or assistance in determining the right rack mount solution for your business, call us at 866-207-6631, visit our web site, or email us at sales@rackmountsolutions.net.

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