Journals and sleeves normally fall into three categories for aerospace use; lined, plain, and sintered/impregnated. Lined journals take the form of a metal backing which is normally steel, aluminum or bronze alloy with a lining placed around the bore. The lining is usually a PTFE derivative held within a cloth matrix. Alternatively the lining can take the form of a polymer compound mated onto a bronze backing. The combinations are extremely varied with each having properties which excel in certain areas. For example some of the stronger liner types produced by Ampep, Sarma, RWG Frankenjura, US Bearing, Khar and Kamatics are well suited to helicopter applications (high load, high cycle frequency environments), whilst others made by manufacturers such as Glacier are more suited to slower paced.

Inch size lined aerospace journals can be called up using the Mil-Spec nomenclature (denoted M……). For example the M81934/1 (plain journal) and M81934/2 (flanged plain journal) can be called with an associated dash number denoting bore, backing material and length. For example a M81934/1-06C008 would denote a plain journal (no flange) with a 6/32” bore, steel backing (denoted by the “C”) and 8/32” in length. This system has been in place for many years although it has recently been superceded by the “AS” system which is kept by the SAE.

Metric lined bearings are not included in the MS or AS specifications and usually fall into the NSA or EN series bearing types. The use of plain non-lined bearings on airframes is prolific. Either being used as true bearing supports or just sacrificial sleeves (spherical bearing locators). There are many plain-bearing manufacturers who make journals that conform to NSA, BACB, NAS or MS standards.