{"id":11400,"date":"2026-09-25T20:02:08","date_gmt":"2026-09-25T16:02:08","guid":{"rendered":"https:\/\/iesco.ge\/?p=11400"},"modified":"2026-09-25T21:02:07","modified_gmt":"2026-09-25T17:02:07","slug":"how-to-choose-a-bearing","status":"publish","type":"post","link":"https:\/\/iesco.ge\/en\/how-to-choose-a-bearing\/","title":{"rendered":"How to Choose a Bearing: Reading Bearing Numbers and Picking the Right Type"},"content":{"rendered":"

A bearing is one of the most “invisible” parts of any machine \u2014 until it fails. Noise, heat, vibration and finally a damaged shaft or motor winding often start with one small mistake: the wrong bearing. There are three typical reasons a bearing wears out early: the wrong type or clearance<\/strong>, a poor-quality (counterfeit) product<\/strong> and incorrect mounting or lubrication<\/strong>. This article covers all three \u2014 and shows how to read a bearing number so you pick the right bearing the first time.<\/p>\n

1. Bearing types \u2014 which one works where<\/h2>\n

Before reading the number, you need to know which type<\/strong> you need. In industrial equipment (electric motors<\/a>, pumps, compressors<\/a>, gearboxes, conveyors, machine tools) you will mostly meet seven types:<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n
Type<\/th>\nNumber starts with<\/th>\nWhere it is used<\/th>\nWhat it handles well<\/th>\n<\/tr>\n<\/thead>\n
Deep groove ball<\/td>\n60xx, 62xx, 63xx<\/td>\nElectric motors, fans, pumps, compressors<\/td>\nRadial load, high speed; light axial load<\/td>\n<\/tr>\n
Tapered roller<\/td>\n30xxx, 31xxx, 32xxx, 33xxx<\/td>\nGearboxes, axles, machine-tool spindles<\/td>\nHeavy radial and<\/strong> axial load at the same time<\/td>\n<\/tr>\n
Cylindrical roller<\/td>\nNU, NJ, NUP, N<\/td>\nLarge electric motors, compressors, gearboxes<\/td>\nVery heavy radial load, high speed<\/td>\n<\/tr>\n
Angular contact ball<\/td>\n72xx, 73xx (B, C, AC)<\/td>\nSpindles, centrifugal pumps, ball screws<\/td>\nAxial load in one direction + radial; precision<\/td>\n<\/tr>\n
Thrust ball<\/td>\n511xx, 512xx, 513xx<\/td>\nVertical shafts, support units<\/td>\nAxial load only, low speed<\/td>\n<\/tr>\n
Needle roller<\/td>\nHK, NK, NA, RNA<\/td>\nCompact units with little space<\/td>\nHeavy radial load on a small diameter<\/td>\n<\/tr>\n
Spherical \/ self-aligning<\/td>\n22xxx, 23xxx; 12xx, 13xx<\/td>\nVibrating machinery, conveyor pulleys<\/td>\nShaft misalignment<\/strong> and vibration<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n

Rule of thumb: electric motors and pumps \u2014 deep groove ball (6xxx)<\/strong>; gearboxes and axles with load in both directions \u2014 tapered (3xxxx)<\/strong>; heavy radial load \u2014 cylindrical (NU)<\/strong>. If the shaft and housing are not on one axis (misalignment) \u2014 spherical.<\/p>\n

2. Roller bearings: tapered and cylindrical<\/h2>\n

When the load is heavy, a ball bearing is no longer enough: a ball touches the ring at a point, a roller along a whole line. Two roller types are the most common in industrial equipment.<\/p>\n

\"Tapered
Tapered (cone + cup) and cylindrical NU \u2014 both are roller bearings, both are separable<\/figcaption><\/figure>\n

Tapered (30xxx\u201333xxx)<\/strong> bearings consist of two parts \u2014 the inner ring with rollers (cone) and the outer ring (cup). They carry radial and axial load together, but axial load in one direction only \u2014 so they are mounted in pairs<\/strong> or with preload<\/strong>: in gearboxes, axles and machine-tool spindles. Numbering: last two digits \u00d7 5 = bore diameter (30212<\/code> \u2192 60 mm). KOYO bearings often carry the suffix JR<\/code> (KOYO’s own internal-design code) or HI-CAP<\/code> (high-capacity series).<\/p>\n

Cylindrical (NU, N, NJ, NUP)<\/strong> \u2014 the rollers are parallel to the shaft, so they carry very heavy radial load at high speed, but little or no axial load. The letters tell you which ring has ribs<\/strong> (the side shoulders that guide the rollers):<\/p>\n

\n\n\n\n\n\n\n\n\n
Type<\/th>\nRibs<\/th>\nAxial movement of the shaft<\/th>\nWhere it is used<\/th>\n<\/tr>\n<\/thead>\n
NU<\/strong><\/td>\nTwo on the outer ring, none on the inner<\/td>\nFree in both directions<\/td>\nElectric motors, compressors \u2014 paired with a ball bearing, for thermal expansion of the shaft<\/td>\n<\/tr>\n
N<\/strong><\/td>\nTwo on the inner ring, none on the outer<\/td>\nFree in both directions<\/td>\nThe same, where the free ring is better on the housing side<\/td>\n<\/tr>\n
NJ<\/strong><\/td>\nTwo on the outer, one on the inner<\/td>\nLocked in one direction<\/td>\nAxial load in one direction<\/td>\n<\/tr>\n
NUP<\/strong><\/td>\nTwo on each ring (one on a loose rib ring)<\/td>\nLocked in both directions<\/td>\nLocating the shaft<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n

The bore is read the same way: NU208<\/code> \u2192 08 × 5 = 40 mm; the suffix E<\/strong> means a reinforced design with more rollers.<\/p>\n

Tip:<\/strong> replacing an NU with an NJ or NUP “of the same size” is a common mistake \u2014 the shaft can no longer expand, the bearing is pinched axially and overheats. Both types are separable and their rings are mounted separately: do not mix the parts of a new bearing with an old one or with another set.<\/p>\n

3. Decoding a bearing number \u2014 example 6208 ZZ C3<\/code><\/h2>\n

Metric numbers of ball and roller bearings follow one logic. Take the most common electric-motor bearing \u2014 6208 ZZ C3<\/strong>:<\/p>\n

\"How
6208 ZZ C3 \u2014 type, series, bore diameter, shields and clearance<\/figcaption><\/figure>\n
\n\n\n\n\n\n\n\n\n\n
Part<\/th>\nMeaning<\/th>\n<\/tr>\n<\/thead>\n
6<\/strong><\/td>\nType: deep groove ball bearing<\/td>\n<\/tr>\n
2<\/strong><\/td>\nDimension series: 0 \u2014 extra light, 2 \u2014 light, 3 \u2014 medium (63xx is thicker and carries more than 62xx with the same bore)<\/td>\n<\/tr>\n
08<\/strong><\/td>\nBore diameter: 08 × 5 = 40 mm<\/strong><\/td>\n<\/tr>\n
ZZ<\/strong><\/td>\nMetal<\/strong> shields on both sides<\/td>\n<\/tr>\n
C3<\/strong><\/td>\nGreater-than-normal radial clearance<\/strong><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n

Bore diameter rule (last two digits):<\/p>\n

\n\n\n\n\n\n
Code<\/th>\n00<\/th>\n01<\/th>\n02<\/th>\n03<\/th>\n04 and up<\/th>\n<\/tr>\n<\/thead>\n
Bore<\/td>\n10 mm<\/td>\n12 mm<\/td>\n15 mm<\/td>\n17 mm<\/td>\ncode × 5 (05 \u2192 25 mm, 12 \u2192 60 mm)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n

Common suffixes:<\/strong><\/p>\n