A linear motion bearing or slide is a bearing designed to provide free motion in one dimension. There are many different types of linear motion bearings and this family of products is generally broken down into two sub-categories: rolling-element and plain.

Rolling-element bearing

A rolling-element bearing is generally composed of a sleeve-like outer ring and several rows of balls retained by cages. The cages were originally machined from solid metal and were quickly replaced by stampings. It features smooth motion, low friction, high rigidity and long life. They are economical, and easy to maintain and replace. Thomson (currently owned by Danaher) is generally given credit for first producing [what is now known as] a linear ball bearing.

• Rolling-element bearings can only run on hardened steel or stainless steel shafting (raceways).
• Rolling-element bearings are more rigid than plane bearings.
• Rolling-element bearings do not handle contamination well and require seals/scrapers.
• Rolling-element bearings require lubrication.

Plain bearing

A plain bearing/bushing is very similar in design to a rolling-element bearing/bushing, but it uses no balls. Plain bearings are further broken down into several families: bronze bushings, metal/polymer bushings and all-polymer bushings. All metal (usually bronze) bushings were the start of this family of bearings and these types of bearings have been used since the Middle Ages. Babbitt bearings also fall into this product group. These types of bearings are still commonly used today. The second category is the metal + polymer bearing. These types of bearings have been used since the early 1980s when Pacific Bearing introduced its Simplicity Self-Lubricating Linear Bearing. This type of bearing uses an aluminum, steel or stainless steel outer shell and a piece of polymer or fluoro-polymer as a liner. This type of liner is usually made of Teflon® (to reduce friction) plus fillers (to increase life). The hard outer shell in combination with the enhanced polymer liner give this type of bearing a superior performance advantage over the other two types of bearings/bushings in this category. The third type of bushing/bearing is the all-polymer bushing. This bearing is used primarily in high-volume applications where cost is critical and the cost per bushing must be driven down to only a few pennies per part. Automated injection-molding machines allow this type of production at a reduced cost.

• Plain bearings can run on hardened steel or stainless steel shafting (raceways), or can be run on hard-anodized aluminum or soft steel or aluminum. The specific type of polymer/fluoro-polymer will determine what hardness is allowed.
• Plain bearings are less rigid than rolling-element bearings.
• Plain bearings handle contamination well and often do not need seals/scrapers.
• Plain bearings generally handle a wider temperature range than rolling-element bearings
• Plain bearings do not require oil or lubrication (often it can be used to increase performance characteristics)

NOTE: "Plane bearings" and "plain bearings" are often confused. Searches for "plain" bearings yield far more results. The misspelling of "plain" and "plane" is quite common. The following paragraph confirms the misspelling: (the following paragraph is included because of its educational/historical value, even though it is inaccurate)

The term "plain bearing" is of relatively recent usage and appears in technical literature such as isolated cases in Japanese patents, and SAE document titles by Japanese authors. A search of patent applications only returns two patents using the term and a search of SAE papers only returns a single paper with the term in its title. The term is also used by Japanese manufactures such as Yamaha and Makita in their parts nomenclature. There are also occasional mentions of the term in European publications. In American engineering practice these bearings are referred to as journal bearings, sleeve bearings or bushing bearings, and a search of index listings of engineering handbooks and reference materials for machinists will show no listings of or reference to "plane bearings". The usage has begun to appear in advertising materials from some bearing vendors only in recent years.

Source: Wikipedia.org