Cage nuts are an essential fastener used to mount equipment in standard server racks in data centers. Cage nuts remain the universal standard across the industry because of their simplicity, strength, and compatibility.
More importantly, cage nuts convert square holes to round! Here's how they work, how to install them, cage nut application calculations and how many server racks are in a data center.
What Are Cage Nuts
A cage nut is a small, spring-steel clip with a threaded nut in the center that is designed to snap into the square holes of a rack's mounting rails. This creates a threaded anchor point where none existed before.
How Do Cage Nuts Work On Server Racks?
Most server rack rails in data centers are made from thin sheet metal that has uniform square holes punched along their length. Cage nuts for data center server racks provide the necessary thread depth and strength to secure heavy equipment, as the server rack’s sheet metal is too thin to hold threads on its own.
On a properly built rack, servers are essentially floating in mid-air, suspended by their ears and slide rails — there's open airflow above and below each unit, which is intentional for cooling.
How Many Cage Nuts Per Server Rack?
By calculating the number of units, you can figure out how many cage nuts you will need to build the rack.
Per Rack Unit (U):
- Each U has 4 holes (2 on each vertical rail, front and back)
- Each hole can take 1 cage nut
- So a fully populated U uses 4 cage nuts
Per Full Rack:
- A standard rack is 42U tall
- Fully populated: 42U × 4 holes = 168 cage nuts maximum
- In practice, not every U is used, and some equipment (like patch panels or PDUs) may use fewer mounting points
- A typical rack in active use might use 50–120 cage nuts, depending on how densely it's populated. A full 42U rack will use 168 cage nuts.
How are Cage Nuts installed into server racks?
Most common rack-mount servers are built with integral ears or flanges that are welded or bolted to the chassis. Those ears have pre-drilled holes that align with cage nuts in the rail.
The server is held in place once the screw goes through the ear and into the cage nut, and essentially hangs from the front rail by those screws. And that is why strong, dependable cage nuts for data center server racks are so important!
Simple steps to install cage nuts into server racks:
- Locate the correct hole positions — Equipment is measured in "rack units" (U), where 1U = 1.75 inches. You identify the row of holes corresponding to where the equipment will sit.
- Orient the cage nut — The nut has a slight lip on two sides. You hook one side of the lip into the square hole first.
- Snap it in — Using a cage nut insertion tool (or carefully with a flathead screwdriver), you lever the opposite lip over the edge of the hole until it snaps into place. The spring tension holds it firmly against the rail.
- Repeat — Typically 4–8 cage nuts per piece of equipment (matching holes on the front rails, and sometimes rear rails too).
- Once the cage nuts are in place, the equipment (server, switch, patch panel, etc.) is slid onto the rails and its mounting ears align with the cage nuts. Standard M6, #10-32 or #12-24 screws are then driven into the cage nuts to secure everything.
Other installation tips:
Use a cage nut tool — The tool makes inserting the cage nuts easy and risk-free, as you can cut your fingers installing them.
Plan your layout first — It is much easier to install cage nuts before adjacent equipment is in the rack.
Count your U-space carefully — Misplacing cage nuts by even one hole means the screw holes won't line up.
Match the thread standard — Most modern racks use M6 cage nuts, but others equipment uses #10-32 or #12-24. They look similar but aren't interchangeable.
Attach the front and rear rails — Heavy equipment like servers often needs to be secured at both the front and rear rails for stability and airflow management.
The key takeaway: most holes in a typical rack stay empty — you only install cage nuts where you're actually mounting something.
What screws are used with Cage Nuts?
M6 screws
M6 screws are metric fasteners with a 6mm diameter. The standard metric rack screw, designated M6 x 1, follows a straightforward naming convention: "M" denotes that it is metric, "6" represents the outer diameter in millimeters, and "1" indicates the spacing between neighboring threads, also measured in millimeters. An M6 screw can be easily identified by measuring its diameter — it will measure 6mm, or just over 7/32 of an inch (0.228″).
#10-32 screws
The 10-32 designation comes from the Unified and American Screw Thread. In this designation, "10" simply serves as a size identifier with no inherent numerical value, while "32" indicates that the screw has 32 threads per inch. To recognize a 10-32 screw, you can measure its diameter with a ruler — it will measure precisely 3/16 of an inch.
#12-24 screws
The 12-24 thread type is most commonly found in pre-threaded racks. These fasteners are slightly larger than 10-32 screws and feature coarser threading. Like the 10-32 screw, the "12" acts purely as a size identifier with no inherent numerical value, while "24" indicates the screw has 24 threads per inch — fewer than both the 10-32 and M6 standards. A 12-24 screw can be identified by measuring its diameter with a ruler, which will come in at just under 7/32 of an inch (5.6mm).
How Many Server Racks are in a Data Center?
It all depends on the scale of the operation - its size and purpose. It can be anywhere from a small amount to over 100,000. Here are some numbers to consider:
- A typical rack holds 20–40 servers
- A standard data center "row" might have 10–20 racks
- A hyperscale campus can span multiple buildings, each with thousands of racks
Small/Edge Data Centers: 1–10 racks, often used by small businesses or as local edge computing nodes.
Mid-size Enterprise Data Centers: 10–100 racks, typical for a single company's private facility.
Large Enterprise/Colocation Data Centers: 100–1,000+ racks, serving multiple tenants or large organizations.
Hyperscale Data Centers (Google, Amazon, Meta, Microsoft): Tens of thousands of racks — some facilities house 50,000–100,000+ racks across millions of square feet.
Cage Nuts By AdvanceBasics
Proudly manufactured in the USA, the AdvanceBasics line of cage nuts are an affordable and strong solution when building server racks. We offer a variety of finishes and sizes of cage nuts including zinc electroplate chrome and black phosphorus & oil.
Advance Components is a master stocking distributor, which means we have cage nuts in stock and ready to ship. We offer custom bagging, shipping and VMI services. Advance is the source for cage nuts for data centers across the country. Contact us for a custom solution or buy online 24/7.