Glossary
Short explanations of the terms that appear most often in technical enquiries, to help you interpret existing designations.
A bearing designation describes the type and size of a rolling bearing using a standardised system (DIN 623-1). In 6310, “6” stands for deep groove ball bearing, “3” for the dimension series and “10” for the bore code. From code 04 upwards, code × 5 gives the bore diameter, in this case 50 mm.
Suffixes follow the basic designation and describe design details: 2RS means seals on both sides, 2Z or ZZ shields on both sides, C3 greater internal clearance. They should always be stated in full when sourcing a replacement.
Internal clearance is the distance by which one bearing ring can move relative to the other in the radial or axial direction. Normal clearance (CN) has no suffix. C3 denotes greater than normal clearance and is often used where the inner ring heats up more in operation or has a tight fit on the shaft, for example in electric motors.
The deep groove ball bearing is the most widely used rolling bearing. It supports radial loads and, to a limited extent, axial loads in both directions, is suitable for high speeds and is available open or with shields or seals.
Cylindrical roller bearings have cylindrical rollers and carry high radial loads. The design depends on the arrangement of the ribs: with NU and N the rings can move axially relative to each other (non-locating bearing), NJ locates the shaft axially in one direction, NUP in both directions.
Tapered roller bearings have tapered rollers and support combined radial and axial loads. As they carry axial loads in one direction only, they are usually mounted in pairs against each other, for example in gearboxes.
A typical shaft arrangement consists of a locating bearing, which guides the shaft axially, and a non-locating bearing, which compensates for length changes caused by thermal expansion. Whether a bearing acts as locating or non-locating affects the choice of design and fit.
A radial shaft seal seals a rotating shaft against a housing. It usually consists of an elastomer with a metal insert and a garter spring that presses the sealing lip onto the shaft. Designs and dimensions are standardised in DIN 3760 and ISO 6194. It is often colloquially called a “Simmerring”, which is a registered trademark.
Type A and AS are designations according to DIN 3760. A has a rubber-covered outside diameter and a spring-loaded sealing lip, AS additionally has a dust lip against external contamination. Types B and BS have a metal outside diameter.
NBR, FKM and PTFE are common seal materials. NBR (nitrile rubber) is standard for mineral oils and greases and typically suitable up to about 100 °C. FKM (fluoroelastomer) withstands temperatures up to about 200 °C and many more aggressive media. PTFE offers high chemical resistance and low friction. These are guide values; the manufacturer’s approval is decisive.
Circumferential speed is the speed of the shaft surface under the sealing lip: v = π · d · n / 60,000 (v in m/s, d = shaft diameter in mm, n = speed in rpm). Example: a 45 mm shaft at 1,450 rpm gives about 3.4 m/s. Together with temperature and medium, it determines the choice of material.
A V-ring is an elastomer ring that sits on the shaft, rotates with it and seals axially against a counterface. It is often used as a pre-seal to keep dirt and splash water away from the bearing and shaft seal.
A repair sleeve is a thin-walled steel sleeve pressed onto a worn shaft to create a new, smooth running surface for the sealing lip. This allows the shaft to be reused without machining.
Pitch is the distance between the centres of two adjacent pins of a chain. It is the most important chain dimension and must match the sprocket. For roller chains to ISO 606, the number before the letter gives the pitch in sixteenths of an inch: 16B means 16/16 inch, i.e. 25.4 mm.
For roller chains to ISO 606, A denotes the American series (DIN 8188) and B the European series (DIN 8187). The number after the hyphen gives the number of strands: -1 for simplex, -2 for duplex and -3 for triplex chains.
Chain elongation is the wear-related lengthening of a chain caused by abrasion in the joints. Replacement is often recommended from about 2 to 3 % elongation; the manufacturer’s specifications are decisive. An elongated chain also wears the sprockets faster.
A scraper chain is the chain of a trough or scraper chain conveyor. Flights attached to the chain pull bulk material such as swarf, mill scale or granulate through an enclosed trough.
A leaf chain consists of alternately arranged plates and pins and has no rollers. It runs over pulleys instead of sprockets and is mainly used for lifting applications such as forklifts and lifting masts. It is standardised in ISO 4347 and DIN 8152.
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