Frequently Asked Questions

Racks 101

Quick Links:

• What is a rack
• What is a Rack Unit (RU)?
• Mounting Types
• Mounting Hardware

What is a Rack?

• Open frame racks are structures onto which equipment is mounted using screws, cage nuts, or other mounting hardware.
• Most rack-mounted electronic equipment have mounting widths of 19” (483 mm) or 23” (584 mm).
• Common uses include servers, telecom, broadcast video, lighting, audio, and scientific lab equipment. 
• When the equipment cannot be rack mounted, Hammond has many other options/accessories to help secure that equipment to the rack.  ie. shelves.

What is a Rack Unit (RU)?

• A rack unit is the unit of measure that the rack industry uses to define vertical space. Often referred to as the number of “U” or “RU” to describe the mounting height of a rack or cabinet.
• 1U = 1¾ inches (44.45 mm) in height. Example: A customer may ask for a 44U rack.
• Rack units are often indicated as a number and/or as a marking.
  
  

Mounting Types

• Equipment can be mounted to racks and cabinets in various ways. There can be;
  • tapped rails,
  • round hole and
  • square hole rails.
• It is important to confirm what type of mounting rails they require.
• Typically, open racks come with tapped holes, whereas larger cabinets meant for heavy servers come with square holes for cage nuts.

Combination Rails

• Combination rails are unique in that they allow you to mount equipment onto the front of the rails but also onto the side of the rail/cabinet. 
• Side mounting is only used when there are front and back rails (set of 4).
• Typically, combination rails are used in industrial, test, and measurement applications or for mounting accessories.
• Hammond has three (3) types of combination rails:
  • The CCR Series is a zinc-plated steel rail that is compatible with our C2, C2RR, and REFK Cabinets.
  • The RCHR Series is powder-coated black and compatible with our RCH Cabinets.
  • The RSRC Series is powder-coated black and compatible with our RS and 1564 Consoles.

Mounting Hardware

• Rack screws are used to attach equipment directly to the tapped rack rails. Several sizes of screws are available, but 10-32, 12-24, and M6 are the most common. 
• Square (cage nut) or round (clip nut) holes on rack rails require the nut plus a screw in order to secure equipment to the mounting rail.   
• With square mounting holes, the screws connect to a removable cage nut placed in the required location on the rail.
• With round holes, the screws thread into a removable clip nut placed in the required location on the rail.