Linear bearing rails provide a smooth, precision, guiding surface on which the rolling element of a linear bearing rides. They are an integral part of linear bearings, typically ordered separately from the rolling element component.
 
Linear bearings are available in many configurations, with differing attributes such as stiffness, smoothness of motion, profile height, cost, material, and rolling element type.  Some of the more common types include crossed roller bearings, linear motion (LM) guides, bushing style bearings (plain bearings or with balls), needle roller bearings, roller bearings, splined shaft bearings, and various guide wheel configurations.

Rail Types

Rail choices for linear bearings include low profile, crossed roller rail, miniature guide, radial or curved, linear motion guide, M/V style rail, round shaft, spline shaft, track system, T shaped, twin shaft, and V-grooved guide.

• Linear guides allow the directional movement of a carriage along their length.
• A low profile guide is a type of linear guide that has a very low horizontal profile.
• Crossed roller bearings consist of a caged roller assembly and two matching guide rails with machined v-groove bearing surfaces.
• Miniature refers simply to the size of the guide and is stated as such by the manufacturer.
• A curved guide is also defined as curvilinear in shape, has specific uses in instrumentation.
• Linear motion guides may also be referred to as linear guide bearings, square rail linear bearings, linear guide ways, or recirculating ball bearings.
• An M/V style rail is a form of linear rail or guide with two mating rails.
• Round shaft linear guides are typically hardened and ground shafts used for bushing style linear bearings.
• A spline shaft has either grooves or tongues machined along its length.
• A track system is a linear guide assembly that combines several rail components into a closed loop system.
• T shaped guides are a form of rectangular guide where the bearing races are extended outward from the top of the support, forming a "T" shape.
• Twin shafts are round, parallel shafts that are located in close proximity with each other.
• V-grooved guides have grooves that are machined along the length of the guide at a 90-degree or other angle, forming a "V" shape and acting as a race for the bearings or rollers to run on.

Video Credit: Bishop-Wisecarver Corporation

An assembly has the linear rail and matched linear bearing packaged together and sold as an assembly.  The supplier, indicating that the component has been manufactured to tighter tolerances than their standard linear guide product, has designated a precision grade rail as such.

Materials and Features

Material choices for linear bearing rails include aluminum, polymer or plastic, stainless steel, or steel.  Material features include corrosion resistance, case hardened, thru hardened, and not hardened.  Important dimensions to consider include guide width or diameter and guide length.  Features common to linear guides and rails include continuously or intermittently supported, end-supported, clean room ruse, pre-drilled holes, self-aligning, and vacuum compatible.

Standards

• ISO 12090-1 - ROLLING BEARINGS - PROFILED RAIL GUIDES FOR LINEAR MOTION ROLLING BEARINGS - PART 1: BOUNDARY DIMENSIONS AND TOLERANCES FOR SERIES 1, 2 AND 3
• ISO 12090-2 - ROLLING BEARINGS - PROFILED RAIL GUIDES FOR LINEAR MOTION ROLLING BEARINGS - PART 2: BOUNDARY DIMENSIONS AND TOLERANCES FOR SERIES 4 AND 5

Image credits:

Schneeber Inc. | NSK Precision America, Inc. | Isotech, Inc.