Home>Products>angular contact ball bearings>ISO 7209 ADT angular contact ball bearings
ISO 7209 ADT MODELS
Need a CAD or 3D Model?
ISO 7209 ADT angular contact ball bearings
category
angular contact ball bearings
ISO 7209 ADT Bearing SPECIFICATIONS
Online shopping ISO 7209 ADT angular contact ball bearings from a great selection NTN BEARING CORP.OF AMERICA 25 mm d at Store. ... angular contact ball bearings Accessories.
- ISO
7209 ADT
- Pillow Block
- 0.0
- N/A
- 10.987
- M06288
- 4
- Concentric Collar
- 4 Bolt Pillow Block
-
NTN BEARING CORP.OF AMERICA2020-07-10 09:46:19
Welcome to my shop! Glad to serve you! Please send your question!
ISO 7209 ADT angular contact ball bearings Technical information
- Pillow Block
- 0.0
- N/A
- 10.987
- M06288
- 4
- Concentric Collar
- 4 Bolt Pillow Block
- Spherical Roller Bearing
- Cast Iron
- Non-expansion
- 1/2 Inch
- Yes
- 2207U
- Heavy Contact
- 1 Piece Solid
- Inch
- Double Row | Single Collar | Two Auxiliary End Cap | With Set Screw
- 4 Bolt Pillow Block; 2-7/16" Bore; 2-3/4" Base to Center Height; Concentric Collar Mount; Spherical Roller Bearing; Relubricatable; Cast Iron; Heavy Contact; Non-expansion
- 31171511
- 8483.20.40.80
- Bearing
- Pillow Block
- BMA2207F
- 6891738
- 16.6
- 7.3 Inch | 184 Millimeter
- 2.75 Inch | 69.85 Millimeter
- 2.438 Inch | 61.925 Millimeter
- 0 Inch | 0Millimeter
- 3.5 Inch | 88.9 Millimeter
- 0 Inch | 0Millimeter
- 7.1 Inch | 181Millimeter
ISO 7209 ADT ISO 7209 ADT angular contact ball bearings Cross reference
Frequently bought ISO 7209 ADT angular contact ball bearings together | |||||||||
---|---|---|---|---|---|---|---|---|---|
No. | Brand | T | B | C | a | d | D | D1 | d1 |
SS7209 ACD/P4A | SKF | - | 19 mm | 41 kN | 25 mm | 45 mm | 85 mm | 75,7 mm | 57,3 mm |
SS7209 CD/HCP4A | SKF | - | 19 mm | 42,3 kN | 18 mm | 45 mm | 85 mm | 75,7 mm | 57,3 mm |
SS7209 CD/P4A | SKF | - | 19 mm | 42,3 kN | 18 mm | 45 mm | 85 mm | 75,7 mm | 57,3 mm |
SS7209 ACD/HCP4A | SKF | - | 19 mm | 41 kN | 25 mm | 45 mm | 85 mm | 75,7 mm | 57,3 mm |
S7209 ACD/P4A | SKF | - | 19 mm | - | 24.8 mm | 45 mm | 85 mm | - | - |
S7209 CD/HCP4A | SKF | - | 19 mm | - | 18.3 mm | 45 mm | 85 mm | - | - |
S7209 CD/P4A | SKF | - | 19 mm | - | 18.3 mm | 45 mm | 85 mm | - | - |
S7209B | ZEN | - | 19 mm | 37,2 kN | - | 45 mm | 85 mm | - | - |
S7209 ACD/HCP4A | SKF | - | 19 mm | - | 24.8 mm | 45 mm | 85 mm | - | - |
NP727209-90KA1 | Timken | 20 mm | 20 mm | - | - | 50 mm | 80 mm | - | - |
NP727209/NP106970 | Timken | 20 mm | 20 mm | - | - | 50 mm | 80 mm | - | - |
NTN HUB167-9 angular contact ball bearings | Category:Pillow Block Bearings; Inventory:0.0; Manufacturer Name:REXNORD; Minimum Buy Quantity:N/A; Weight:10.987; Product Group:M06288; Number of Mounting Holes:4; Mounting Method:Concentric Collar; Housing Style:4 Bolt Pillow Block; Rolling Element:Spherical Roller Bearing; Housing Material:Cast Iron; Expansion / Non-expansion:Non-expansion; Mounting Bolts:1/2 Inch; Relubricatable:Yes; Insert Part Number:2207U; Seals:Heavy Contact; Housing Configuration:1 Piece Solid; Inch - Metric:Inch; Other Features:Double Row | Single Collar | Two Auxiliary End Cap | With Set Screw; Long Description:4 Bolt Pillow Block; 2-7/16" Bore; 2-3/4" Base to Center Height; Concentric Collar Mount; Spherical Roller; Category:Pillow Block; UNSPSC:31171511; Harmonized Tariff Code:8483.20.40.80; Noun:Bearing; Keyword String:Pillow Block; Manufacturer Item Number:BMA2207F; Manufacturer Internal Number:6891738; Weight / LBS:16.6; Nominal Bolt Center to Center:7.3 Inch | 184 Millimeter; B:2.75 Inch | 69.85 Millimeter; d:2.438 Inch | 61.925 Millimeter; Bolt Spacing Minimum:0 Inch | 0Millimeter; D:3.5 Inch | 88.9 Millimeter; Bolt Spacing Maximum:0 Inch | 0Millimeter; Actual Bolt Center to Center:7.1 Inch | 181Millimeter; |
55 mm x 80 mm x 13 mm NTN 5S-2LA-HSE911G/GNP42 angular contact ball bearings | Category:Pillow Block Bearings; Inventory:0.0; Manufacturer Name:REXNORD; Minimum Buy Quantity:N/A; Weight:10.987; Product Group:M06288; Number of Mounting Holes:4; Mounting Method:Concentric Collar; Housing Style:4 Bolt Pillow Block; Rolling Element:Spherical Roller Bearing; Housing Material:Cast Iron; Expansion / Non-expansion:Non-expansion; Mounting Bolts:1/2 Inch; Relubricatable:Yes; Insert Part Number:2207U; Seals:Heavy Contact; Housing Configuration:1 Piece Solid; Inch - Metric:Inch; Other Features:Double Row | Single Collar | Two Auxiliary End Cap | With Set Screw; Long Description:4 Bolt Pillow Block; 2-7/16" Bore; 2-3/4" Base to Center Height; Concentric Collar Mount; Spherical Roller; Category:Pillow Block; UNSPSC:31171511; Harmonized Tariff Code:8483.20.40.80; Noun:Bearing; Keyword String:Pillow Block; Manufacturer Item Number:BMA2207F; Manufacturer Internal Number:6891738; Weight / LBS:16.6; Nominal Bolt Center to Center:7.3 Inch | 184 Millimeter; B:2.75 Inch | 69.85 Millimeter; d:2.438 Inch | 61.925 Millimeter; Bolt Spacing Minimum:0 Inch | 0Millimeter; D:3.5 Inch | 88.9 Millimeter; Bolt Spacing Maximum:0 Inch | 0Millimeter; Actual Bolt Center to Center:7.1 Inch | 181Millimeter; |
130 mm x 200 mm x 33 mm NTN 7026DF angular contact ball bearings | Category:Pillow Block Bearings; Inventory:0.0; Manufacturer Name:REXNORD; Minimum Buy Quantity:N/A; Weight:10.987; Product Group:M06288; Number of Mounting Holes:4; Mounting Method:Concentric Collar; Housing Style:4 Bolt Pillow Block; Rolling Element:Spherical Roller Bearing; Housing Material:Cast Iron; Expansion / Non-expansion:Non-expansion; Mounting Bolts:1/2 Inch; Relubricatable:Yes; Insert Part Number:2207U; Seals:Heavy Contact; Housing Configuration:1 Piece Solid; Inch - Metric:Inch; Other Features:Double Row | Single Collar | Two Auxiliary End Cap | With Set Screw; Long Description:4 Bolt Pillow Block; 2-7/16" Bore; 2-3/4" Base to Center Height; Concentric Collar Mount; Spherical Roller; Category:Pillow Block; UNSPSC:31171511; Harmonized Tariff Code:8483.20.40.80; Noun:Bearing; Keyword String:Pillow Block; Manufacturer Item Number:BMA2207F; Manufacturer Internal Number:6891738; Weight / LBS:16.6; Nominal Bolt Center to Center:7.3 Inch | 184 Millimeter; B:2.75 Inch | 69.85 Millimeter; d:2.438 Inch | 61.925 Millimeter; Bolt Spacing Minimum:0 Inch | 0Millimeter; D:3.5 Inch | 88.9 Millimeter; Bolt Spacing Maximum:0 Inch | 0Millimeter; Actual Bolt Center to Center:7.1 Inch | 181Millimeter; |
80 mm x 125 mm x 22 mm NTN 5S-2LA-BNS016ADLLBG/GNP42 angular contact ball bearings | Category:Pillow Block Bearings; Inventory:0.0; Manufacturer Name:REXNORD; Minimum Buy Quantity:N/A; Weight:10.987; Product Group:M06288; Number of Mounting Holes:4; Mounting Method:Concentric Collar; Housing Style:4 Bolt Pillow Block; Rolling Element:Spherical Roller Bearing; Housing Material:Cast Iron; Expansion / Non-expansion:Non-expansion; Mounting Bolts:1/2 Inch; Relubricatable:Yes; Insert Part Number:2207U; Seals:Heavy Contact; Housing Configuration:1 Piece Solid; Inch - Metric:Inch; Other Features:Double Row | Single Collar | Two Auxiliary End Cap | With Set Screw; Long Description:4 Bolt Pillow Block; 2-7/16" Bore; 2-3/4" Base to Center Height; Concentric Collar Mount; Spherical Roller; Category:Pillow Block; UNSPSC:31171511; Harmonized Tariff Code:8483.20.40.80; Noun:Bearing; Keyword String:Pillow Block; Manufacturer Item Number:BMA2207F; Manufacturer Internal Number:6891738; Weight / LBS:16.6; Nominal Bolt Center to Center:7.3 Inch | 184 Millimeter; B:2.75 Inch | 69.85 Millimeter; d:2.438 Inch | 61.925 Millimeter; Bolt Spacing Minimum:0 Inch | 0Millimeter; D:3.5 Inch | 88.9 Millimeter; Bolt Spacing Maximum:0 Inch | 0Millimeter; Actual Bolt Center to Center:7.1 Inch | 181Millimeter; |
200 mm x 310 mm x 51 mm NTN 7040DF angular contact ball bearings | Category:Pillow Block Bearings; Inventory:0.0; Manufacturer Name:REXNORD; Minimum Buy Quantity:N/A; Weight:10.987; Product Group:M06288; Number of Mounting Holes:4; Mounting Method:Concentric Collar; Housing Style:4 Bolt Pillow Block; Rolling Element:Spherical Roller Bearing; Housing Material:Cast Iron; Expansion / Non-expansion:Non-expansion; Mounting Bolts:1/2 Inch; Relubricatable:Yes; Insert Part Number:2207U; Seals:Heavy Contact; Housing Configuration:1 Piece Solid; Inch - Metric:Inch; Other Features:Double Row | Single Collar | Two Auxiliary End Cap | With Set Screw; Long Description:4 Bolt Pillow Block; 2-7/16" Bore; 2-3/4" Base to Center Height; Concentric Collar Mount; Spherical Roller; Category:Pillow Block; UNSPSC:31171511; Harmonized Tariff Code:8483.20.40.80; Noun:Bearing; Keyword String:Pillow Block; Manufacturer Item Number:BMA2207F; Manufacturer Internal Number:6891738; Weight / LBS:16.6; Nominal Bolt Center to Center:7.3 Inch | 184 Millimeter; B:2.75 Inch | 69.85 Millimeter; d:2.438 Inch | 61.925 Millimeter; Bolt Spacing Minimum:0 Inch | 0Millimeter; D:3.5 Inch | 88.9 Millimeter; Bolt Spacing Maximum:0 Inch | 0Millimeter; Actual Bolt Center to Center:7.1 Inch | 181Millimeter; |
40 mm x 52 mm x 7 mm NTN 7808C angular contact ball bearings | Category:Pillow Block Bearings; Inventory:0.0; Manufacturer Name:REXNORD; Minimum Buy Quantity:N/A; Weight:10.987; Product Group:M06288; Number of Mounting Holes:4; Mounting Method:Concentric Collar; Housing Style:4 Bolt Pillow Block; Rolling Element:Spherical Roller Bearing; Housing Material:Cast Iron; Expansion / Non-expansion:Non-expansion; Mounting Bolts:1/2 Inch; Relubricatable:Yes; Insert Part Number:2207U; Seals:Heavy Contact; Housing Configuration:1 Piece Solid; Inch - Metric:Inch; Other Features:Double Row | Single Collar | Two Auxiliary End Cap | With Set Screw; Long Description:4 Bolt Pillow Block; 2-7/16" Bore; 2-3/4" Base to Center Height; Concentric Collar Mount; Spherical Roller; Category:Pillow Block; UNSPSC:31171511; Harmonized Tariff Code:8483.20.40.80; Noun:Bearing; Keyword String:Pillow Block; Manufacturer Item Number:BMA2207F; Manufacturer Internal Number:6891738; Weight / LBS:16.6; Nominal Bolt Center to Center:7.3 Inch | 184 Millimeter; B:2.75 Inch | 69.85 Millimeter; d:2.438 Inch | 61.925 Millimeter; Bolt Spacing Minimum:0 Inch | 0Millimeter; D:3.5 Inch | 88.9 Millimeter; Bolt Spacing Maximum:0 Inch | 0Millimeter; Actual Bolt Center to Center:7.1 Inch | 181Millimeter; |
25 mm x 47 mm x 12 mm NTN BNT005 angular contact ball bearings | Category:Pillow Block Bearings; Inventory:0.0; Manufacturer Name:REXNORD; Minimum Buy Quantity:N/A; Weight:10.987; Product Group:M06288; Number of Mounting Holes:4; Mounting Method:Concentric Collar; Housing Style:4 Bolt Pillow Block; Rolling Element:Spherical Roller Bearing; Housing Material:Cast Iron; Expansion / Non-expansion:Non-expansion; Mounting Bolts:1/2 Inch; Relubricatable:Yes; Insert Part Number:2207U; Seals:Heavy Contact; Housing Configuration:1 Piece Solid; Inch - Metric:Inch; Other Features:Double Row | Single Collar | Two Auxiliary End Cap | With Set Screw; Long Description:4 Bolt Pillow Block; 2-7/16" Bore; 2-3/4" Base to Center Height; Concentric Collar Mount; Spherical Roller; Category:Pillow Block; UNSPSC:31171511; Harmonized Tariff Code:8483.20.40.80; Noun:Bearing; Keyword String:Pillow Block; Manufacturer Item Number:BMA2207F; Manufacturer Internal Number:6891738; Weight / LBS:16.6; Nominal Bolt Center to Center:7.3 Inch | 184 Millimeter; B:2.75 Inch | 69.85 Millimeter; d:2.438 Inch | 61.925 Millimeter; Bolt Spacing Minimum:0 Inch | 0Millimeter; D:3.5 Inch | 88.9 Millimeter; Bolt Spacing Maximum:0 Inch | 0Millimeter; Actual Bolt Center to Center:7.1 Inch | 181Millimeter; |
15 mm x 28 mm x 7 mm NTN 7902UADG/GNP42 angular contact ball bearings | Category:Pillow Block Bearings; Inventory:0.0; Manufacturer Name:REXNORD; Minimum Buy Quantity:N/A; Weight:10.987; Product Group:M06288; Number of Mounting Holes:4; Mounting Method:Concentric Collar; Housing Style:4 Bolt Pillow Block; Rolling Element:Spherical Roller Bearing; Housing Material:Cast Iron; Expansion / Non-expansion:Non-expansion; Mounting Bolts:1/2 Inch; Relubricatable:Yes; Insert Part Number:2207U; Seals:Heavy Contact; Housing Configuration:1 Piece Solid; Inch - Metric:Inch; Other Features:Double Row | Single Collar | Two Auxiliary End Cap | With Set Screw; Long Description:4 Bolt Pillow Block; 2-7/16" Bore; 2-3/4" Base to Center Height; Concentric Collar Mount; Spherical Roller; Category:Pillow Block; UNSPSC:31171511; Harmonized Tariff Code:8483.20.40.80; Noun:Bearing; Keyword String:Pillow Block; Manufacturer Item Number:BMA2207F; Manufacturer Internal Number:6891738; Weight / LBS:16.6; Nominal Bolt Center to Center:7.3 Inch | 184 Millimeter; B:2.75 Inch | 69.85 Millimeter; d:2.438 Inch | 61.925 Millimeter; Bolt Spacing Minimum:0 Inch | 0Millimeter; D:3.5 Inch | 88.9 Millimeter; Bolt Spacing Maximum:0 Inch | 0Millimeter; Actual Bolt Center to Center:7.1 Inch | 181Millimeter; |
12 mm x 32 mm x 10 mm NTN 7201CGD2/GLP4 angular contact ball bearings | Category:Pillow Block Bearings; Inventory:0.0; Manufacturer Name:REXNORD; Minimum Buy Quantity:N/A; Weight:10.987; Product Group:M06288; Number of Mounting Holes:4; Mounting Method:Concentric Collar; Housing Style:4 Bolt Pillow Block; Rolling Element:Spherical Roller Bearing; Housing Material:Cast Iron; Expansion / Non-expansion:Non-expansion; Mounting Bolts:1/2 Inch; Relubricatable:Yes; Insert Part Number:2207U; Seals:Heavy Contact; Housing Configuration:1 Piece Solid; Inch - Metric:Inch; Other Features:Double Row | Single Collar | Two Auxiliary End Cap | With Set Screw; Long Description:4 Bolt Pillow Block; 2-7/16" Bore; 2-3/4" Base to Center Height; Concentric Collar Mount; Spherical Roller; Category:Pillow Block; UNSPSC:31171511; Harmonized Tariff Code:8483.20.40.80; Noun:Bearing; Keyword String:Pillow Block; Manufacturer Item Number:BMA2207F; Manufacturer Internal Number:6891738; Weight / LBS:16.6; Nominal Bolt Center to Center:7.3 Inch | 184 Millimeter; B:2.75 Inch | 69.85 Millimeter; d:2.438 Inch | 61.925 Millimeter; Bolt Spacing Minimum:0 Inch | 0Millimeter; D:3.5 Inch | 88.9 Millimeter; Bolt Spacing Maximum:0 Inch | 0Millimeter; Actual Bolt Center to Center:7.1 Inch | 181Millimeter; |
38 mm x 72 mm x 40 mm NTN AU0810-1LXL/L260 angular contact ball bearings | Category:Pillow Block Bearings; Inventory:0.0; Manufacturer Name:REXNORD; Minimum Buy Quantity:N/A; Weight:10.987; Product Group:M06288; Number of Mounting Holes:4; Mounting Method:Concentric Collar; Housing Style:4 Bolt Pillow Block; Rolling Element:Spherical Roller Bearing; Housing Material:Cast Iron; Expansion / Non-expansion:Non-expansion; Mounting Bolts:1/2 Inch; Relubricatable:Yes; Insert Part Number:2207U; Seals:Heavy Contact; Housing Configuration:1 Piece Solid; Inch - Metric:Inch; Other Features:Double Row | Single Collar | Two Auxiliary End Cap | With Set Screw; Long Description:4 Bolt Pillow Block; 2-7/16" Bore; 2-3/4" Base to Center Height; Concentric Collar Mount; Spherical Roller; Category:Pillow Block; UNSPSC:31171511; Harmonized Tariff Code:8483.20.40.80; Noun:Bearing; Keyword String:Pillow Block; Manufacturer Item Number:BMA2207F; Manufacturer Internal Number:6891738; Weight / LBS:16.6; Nominal Bolt Center to Center:7.3 Inch | 184 Millimeter; B:2.75 Inch | 69.85 Millimeter; d:2.438 Inch | 61.925 Millimeter; Bolt Spacing Minimum:0 Inch | 0Millimeter; D:3.5 Inch | 88.9 Millimeter; Bolt Spacing Maximum:0 Inch | 0Millimeter; Actual Bolt Center to Center:7.1 Inch | 181Millimeter; |
ISO 7209 ADT angular contact ball bearings Video
ISO 7209 ADT angular contact ball bearings - 7209 ADT bearing
ISO 7209 ADT angular contact ball bearings manufacturer and global supplier of reliable ball and roller ... ISO 7209 ADT angular contact ball bearings Industries
7209 ADT bearing - ISO 7209 ADT angular contact ball bearings
ISO 7209 ADT angular contact ball bearings manufacturer and global supplier of reliable ball and roller ... ISO 7209 ADT angular contact ball bearings Industries
Product Categories - BM Bearing Power Machinery Co., Ltd. of
280 mm x 350 mm x 69 mm ISO NA4856 ISO Bearings · ISO 7214 ADT ISO Bearings ... 45 mm x 85 mm x 19 mm ISO 7209 A ISO Bearings · 1000 mm x 1220
Buy ISO 7209 ADT angular contact ball bearings - NTN Mettmann
ISO 7209 ADT angular contact ball bearings, Units and Housings CAD models , ISO Bearing Manufacturing Service . Square Type Flange Shape Get Your Free
Buy ISO 7207 ADT ISO Bearing - DAF Mechanical&Electrical
Shop ISO 7207 ADT ISO Bearing huge online discount ISO Bearing 3000 rpm ... 7209 B ISO Bearing · 47 mm x 85 mm x 45 mm 47 mm x 85 mm x 45 mm ISO
Buy ISO 7315 ADT ISO Bearing - DAF Mechanical&Electrical
Various 401.637 mm H ISO Bearing 711.2 mm L types and sizes to ... ISO 7315 ADT ISO Bearing #1 small image; ISO 7315 ADT ISO Bearing #2 small image ... 45 mm x 85 mm x 19 mm 45 mm x 85 mm x 19 mm ISO 7209 B ISO Bearing
Comprar 45 mm x 85 mm x 19 mm ISO 7209 B Cojinetes De
45 mm x 85 mm x 19 mm ISO 7209 B Cojinetes De Bola De Contacto Angular, modelos CAD de unidades y carcasas, ISO Cojinetes De Bola De Contacto
Implementation Guide
ADT^A08^ADT_A01 ... International Society for Disease Surveillance288 Grove Street #203Braintree, MA 02184-7209 ... -0500||ADT^A03^ADT_A03|NIST-SS-001.12|P|2.5.1|||||||||PH_SS-NoAck^SSSender^2.16.840.1.114222.4.10.3^ISO
Bearing 7209 ADT (ISO) | Size and Specification | Bearings Online
Angular contact ball bearings 7209 ADT. Bearing number : 7209 ADT. Size (mm) : 45x85x38. Brand : ISO. Bore Diameter (mm) : 45. Outer Diameter (mm) : 85
Rodamientos de bolas de contacto angular of page 472
Brand Name Rodamiento 7209 ADT ISO, Model Number Rodamiento 7209 ADT ISO. Min.Order Quantity 1 pcs, Price Negotiable
ISO 7209 ADT INTERCHANGE
angular contact ball bearings Part series 7209 ADT is a potential replacement for these common bearing part numbers:
7209 ADT
7209 ADT
7209 ADT
7209 ADT
7209 ADT
7209 ADT
7209 ADT
7209 ADT
Contact Us

- NTN BEARING CORP.OF AMERICA
- Address1600 E. Bishop Court, P.O. Box 7604,Mount Prospect, IL 60056-7604, U.S.A.
- Phone(Working Time)298-5268
- Fax
ISO 7209 ADT Technical Articles
snl plummer block size catalogue |
backstop bearing skf table |
skf sleeve bearing size pdf file |
angular contact ball bearings CATEGORIES
- angular contact ball bearings
- bearing units
- complex bearings
- cylindrical roller bearings
- deep groove ball bearings
- linear bearings
- needle roller bearings
- plain bearings
- self aligning ball bearings
- spherical roller bearings
- tapered roller bearings
- thrust ball bearings
- thrust roller bearings
- wheel bearings
- 6302 Koyo Bearing
- Timken 6203 2rs C3 Bearing
- NTN6203 Bearing
- Timken Ha500601 Bearing
- NOK SEAL
- SKF OIL SEAL
- TIMKEN NATIONAL SEALS
- wind power bearings
- Taper Roller Bearing
- YRT bearing
- SKF Bearing
- THK Bearings
- KAYDON Bearings
Customers Who Viewed ISO 7209 ADT Bearing Also Viewed
NTN HUB167-9 angular contact ball bearings
130 mm x 200 mm x 33 mm NTN 7026DF angular contact ball bearings
15 mm x 28 mm x 7 mm NTN 7902UADG/GNP42 angular contact ball bearings
80 mm x 125 mm x 22 mm NTN 5S-2LA-BNS016ADLLBG/GNP42 angular contact ball bearings
38 mm x 72 mm x 40 mm NTN AU0810-1LXL/L260 angular contact ball bearings