Deep groove ball bearings are the most-specified radial rolling bearing worldwide, covering ISO 15:2017 metric series from a 3 mm bore up to 400 mm bore and 600 mm outside diameter in the Timken catalogue range [S2].
They carry combined radial and bidirectional axial load in a single row, run at the highest speeds of any ball bearing type, and accept a wider range of closures (Z, ZZ, RS, 2RS, RZ, 2RZ, NR) than any competing geometry [S2]. For pumps, electric motors, gearboxes, and conveyors, this is the default workhorse, and selection mostly reduces to size, tolerance class, internal clearance, and seal choice.
Boundary Dimensions and Series Codes
Boundary dimensions (bore d, outside diameter D, width B) follow ISO 15:2017 for radial rolling bearings, with DIN 625 mirroring the same envelope for 3-1,500 mm bore, 10-1,820 mm OD, 7-140 mm width single-row metric bearings [S5][S2]. Series width families govern capacity versus envelope: 618 and 619 are extra-light, 60 extra-light, 62 light, 63 medium, 64 heavy; 160 extra-light thin-section, 620 light wide, 630 medium wide, 622/623 wider still [S2][S3].
For a 17 mm shaft, the 6203 (40 mm OD, 12 mm width) is the common pick; for 40 mm shaft, the 6208 or 6308 step up. When axial space is tight, the 160xx thin-section series keeps the same bore with a markedly smaller cross-section. A 6307 ZZ example from the NTS data tables lists 35 mm bore, 80 mm OD, 21 mm width, dynamic load rating 33.2 kN, static 19.0 kN, and limiting speeds of 10 000 r/min (grease) / 13 000 r/min (oil) [S7]. When a ball bearing selection lands on a non-standard envelope, the bearing has effectively become a custom component, and the buyer should expect a price step and a lead-time hit.
Load Rating, Speed, and Equivalent Load Math
Dynamic load rating C and static load rating C0 are the two numbers that drive bearing life per ISO 281. The dynamic equivalent radial load is calculated as Pr = X·Fr + Y·Fa, with X, Y, and e taken from the manufacturer's factor f0·Fa/C0 table; for the 63-series deep-groove family, e ranges from 0.19 to 0.28 and Y from 2.30 down to 1.55 as the Fa/Fr ratio rises from 0.172 to 1.38 [S7].
Speed is governed by the cage material, closure type, and lubrication. NSK specifies pressed-steel cages as the default, polyamide resin cages for high-speed duty (lower temperature rise, longer grease life, less noise), and machined brass cages for larger sizes or high mechanical stress [S3]. Open and shielded (Z/ZZ) bearings run faster than contact-sealed (RS/2RS) variants, which trade top speed for contamination protection. A 6307 reference: 10 000 r/min on grease with ZZ shields, 13 000 r/min on oil when open [S7].
Closures, Seals, and Lubricant Selection
Seal choice is a contamination-versus-speed decision, not a marketing preference. NSK groups bearing variants into open, shielded (metal non-contact), contact rubber sealed (low-friction LLU, high-contact LLB), and non-contact LLH; each represents a different balance between ingress protection and friction/torque [S3]. SKF pairs greases to the envelope, with MT47 as the standard fill, MT33 low-friction, GE2 high-temperature, GJN/WTB wide-temperature, and LHT23/VT378 food-grade, the suffix encoding the grease on the bearing code (e.g. 2RS1) [S4].
Timken suffixes follow the same logic: Z is one metal shield, ZZ two shields, RS one contact seal, 2RS two contact seals, RZ/2RZ non-contact seals, NR a snap ring on the outer ring, N a snap ring groove only [S2]. Food, medical, and wash-down duty typically steps up to a stainless-steel bearing (Timken suffix H) or full-ceramic hybrid with silicon nitride balls, where the ceramic option resists aggressive chemicals and reduces wear under marginal lubrication [S3].
Tolerances, Internal Clearance, and Fit Practice
Standard metric deep-groove ball bearings ship to ISO 492 normal tolerance (P0/ABEC-1); precision classes P6, P5, P4, and P2 are available for machine-tool spindles and high-speed electric spindles where runout must stay below a few micrometres. Internal clearance follows a C-scale: C2 tighter than normal, C0 (or unmarked) normal, C3 loose, C4 extra-loose, C5 extra-extra-loose [S2].
Clearance choice tracks the interference fit on the shaft and the temperature differential between inner and outer rings. An electric motor running at 100 °C inner ring versus 70 °C housing needs C3 to avoid negative operating clearance; a precision spindle on a lightly loaded shaft often runs C2. Shaft tolerance is typically k5 or k6 for rotating inner ring, housing H7 or J7 for stationary outer ring, with the exact pairing driven by the load direction and the housing material (steel, cast iron, or light alloy).
Selection Criteria Matrix: When to Pick Which
Four common options cover most duty cycles, and the choice lines up cleanly against four selection criteria:
<b>Open (no closure), pressed-steel cage, C3 clearance</b> - for high-speed electric motors, pumps, and gearboxes where the housing seals the bearing and oil mist or grease purge is controlled externally. Fastest limiting speed, lowest friction, but requires clean assembly.
<b>ZZ (two metal shields), pressed-steel cage, C3</b> - the default for general-purpose industrial applications and conveyor idlers. Pre-lubricated for life in many cases, modest speed loss versus open, robust against casual contamination. A reliable ball bearing pick for OEM volume runs.
<b>2RS (two contact rubber seals), pressed-steel cage, C3</b> - for agricultural machinery, automotive wheel ends, and outdoor equipment exposed to dust, water splash, and mud. Lowest limiting speed of the four, but the highest contamination resistance. Pair with a polyamide or brass cage when radial load is heavy.
<b>Stainless-steel rings + 2RS, polyamide cage, food-grade grease (LHT23/VT378)</b> - for food processing, pharmaceutical, and marine atmospheres. Resists corrosion from wash-down chemicals and chloride exposure, but cuts dynamic load rating by roughly 10-20% versus standard chrome steel at the same envelope [S3][S4].
Who Should NOT Pick a Standard Deep Groove Ball Bearing
Three duty profiles send the buyer to a different bearing type, and ignoring that costs the project a redesign: [S3]
Heavy pure axial load with shaft alignment sensitive to thermal growth: pick an angular contact ball bearing pair (DB or DF mount) or a ball screw support arrangement. A single-row deep-groove bearing has only a small axial capacity relative to its radial figure, and the contact angle is too shallow to lock a precision spindle.
Combined high radial load, misalignment, and shock: a self-aligning ball bearing, spherical roller, or ball spline arrangement absorbs misalignment that a rigid deep-groove geometry cannot. A ScienceDirect worked example runs a 500 N radial load at 10 000 rpm on 11 balls at 100 °C with SAE 30 oil to baseline the contact mechanics; the geometry does not tolerate more than a few minutes of misalignment before edge loading collapses fatigue life [S8].
Clean, dry, abrasive media flow with line pressure above PN16: the bearing is fine, but a ball valve is a separate selection problem. Specifying the wrong component in either role is a frequent procurement error.
Shortlist Logic and Sourcing Signals
Lock the envelope first: bore diameter (with the bore code table: 00=10 mm, 01=12 mm, 02=15 mm, 03=17 mm, 04+=code x 5 mm), then series code (618/619/60/62/63/64 or wide variants), then closure, then cage, then clearance [S2]. Cross-check the C and C0 ratings against the application's equivalent load Pr and the L10h target life; a 6307-class bearing with 33.2 kN C and 19.0 kN C0 will not survive a 20 kN continuous radial load for long, regardless of brand [S7].
For OEM volumes, watch three signals in supplier data: limiting speed with the actual closure/cage combination (not the open-bearing number), full suffix code including internal clearance and grease, and ISO 492 / ABEC tolerance class written out, not implied. NSK, Timken, SKF, and NTS all publish this in their catalogues; sub-tier suppliers often stop at the basic code [S2][S3][S4][S7]. When a ball bearing specification sheet lacks the clearance and tolerance line, treat the quote as incomplete.
Track also standards currency: ISO 15:2017 is the current boundary-dimension reference, and ISO 492 governs tolerance classes. Any quote referencing superseded revisions or omitting the standard number deserves a follow-up question on dimensional interchangeability. ball bearing selection is largely a code-reading exercise once the duty is fixed, and the supplier who can recite the suffix in full is the one to keep on the panel.
This topic is covered further in Squeeze Casting Machine Selection for Energy Equipment.