Inch ball bearings R-series: R188, R144, R166, R2, R3, R4, R6 to R24: bore, OD, width, r + 22 ring-envelope STEP/STL files (1/8 to 1-1/2 in bore) — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/inch-ball-bearings-r-series-r188-r144-r166/ (sheet CC BY 4.0) Basis: NSK inch-series table (r min), NSK R166 / R188ZZ pages, Emerson Bearing R2 to R24 list, checked against TFL Bearing's SKF-designation table; maker pages linked Catalog version: 2026-10-20 Sizes: see table below - R-series ball bearings are the inch-size miniature and small deep-groove bearings: R2 is 1/8 in bore, R4 is 1/4 in bore, R6 is 3/8 in, R8 is 1/2 in. R144, R166 and R188 are the thin-section sizes (1/8 x 1/4, 3/16 x 3/8 and 1/4 x 1/2 in bore x OD). R188 (6.35 x 12.7 x 3.175 open, 4.762 with shields) is a popular size for fidget spinners, small pulleys and RC parts. - Numbers: NSK's inch-series table (R09 to R2A, the first 20 of 41 items, with r min), NSK's R166 and R188ZZ pages, Emerson Bearing's R2 to R24 list in inches (the mm there are the printed inch decimals times 25.4, and they reproduce the SKF and NSK mm values to 0.001 on every shared row), and TFL Bearing's table of the SKF catalogue designations (R1-4 to R6, WR) used as the independent mm check: NSK and TFL agree on every shared row except that NSK prints 4.762 and TFL 4.763 for 3/16 in (4.7625 mm); NSK's value is used. Two Emerson entries disagree with the other sources and are not used: its R3 bore is printed 0.1880 in (3/16 in is 0.1875; TFL / SKF 4.763 mm is shown) and its R4A OD is printed 0.6250 in, the R4 size (TFL / SKF has 19.050 mm, 3/4 in, which is shown; the R4A widths 0.2188 and 0.2812 in agree). - R188: the open bearing is 6.35 x 12.7 x 3.175 mm (TFL, SKDIN: 0.25 x 0.5 x 0.125 in), the ZZ / 2Z / 2RS is 4.762 mm wide (NSK R188ZZ; TFL R188-2Z prints 4.763; MBA R188AZZMC3 4.762). r min 0.15 is NSK's value for the R188ZZ; NSK's R188 open page could not be read, so the open bearing has no printed r here and no file. - Files: 22 ring envelopes for every row that NSK prints with r min (R09 to R2A, R166, R188ZZ): one solid ring, bore, OD, width and corners rounded at r min. No balls, retainer or shield. R3 to R24 and the SKF-only rows have no r read, so they are tables only. - Left out: the other 21 NSK rows (not readable), R4A and larger r min, flanged inch bearings (FR series), thin-section 'RW' sizes, light-duty 1600 series (own page), load ratings, limiting speeds, metric miniature bearings (see the 600/MR series pages). designation bore d, mm OD D, mm width B open, mm width B ZZ / 2RS / 2Z, mm bore x OD (inch, as printed) r min, mm source R09 1.016 3.175 1.191 — — 0.1 NSK R0 1.191 3.967 1.588 2.38 — 0.1 NSK R1 1.397 4.762 1.984 2.779 — 0.1 NSK R1-4 1.984 6.35 2.38 3.571 5/64 x 1/4 0.1 NSK; TFL (SKF) R133 2.38 4.762 1.588 2.38 3/32 x 3/16 0.1 NSK; TFL (SKF) R1-5 2.38 7.938 2.779 3.571 3/32 x 5/16 0.15 NSK; TFL (SKF) R144 3.175 6.35 2.38 2.779 1/8 x 1/4 0.1 NSK; TFL (SKF) R2-5 3.175 7.938 2.779 3.571 1/8 x 5/16 0.1 NSK; TFL (SKF) R2-6 3.175 9.525 2.779 3.571 1/8 x 3/8 0.15 NSK; TFL (SKF) R2 3.175 9.525 3.967 3.967 1/8 x 3/8 0.3 NSK; TFL (SKF); Emerson R2A 3.175 12.7 4.366 4.366 1/8 x 1/2 0.3 NSK; TFL (SKF); Emerson R166 4.762 9.525 3.175 3.175 3/16 x 3/8 0.1 NSK; TFL (SKF) R188 6.35 12.7 3.175 4.762 1/4 x 1/2 0.15 (R188ZZ) NSK; TFL (SKF); SKDIN, MBA R155 3.967 7.938 2.779 3.175 5/32 x 5/16 — TFL (SKF) R156 4.763 7.938 2.779 3.175 3/16 x 5/16 — TFL (SKF) R3 4.763 12.7 3.967 4.978 3/16 x 1/2 — TFL (SKF); Emerson R3A 4.763 15.875 4.978 4.978 3/16 x 5/8 — TFL (SKF) R168 6.35 9.525 3.175 3.175 1/4 x 3/8 — TFL (SKF) R4 6.35 15.875 4.978 4.978 1/4 x 5/8 — TFL (SKF); Emerson R4A 6.35 19.05 5.558 7.142 1/4 x 3/4 — TFL (SKF); Emerson R6 9.525 22.225 5.558 7.142 3/8 x 7/8 — TFL (SKF); Emerson R8 12.7 28.575 6.35 7.938 0.5000 x 1.1250 x 0.2500 / 0.3125 — Emerson (mm = printed inch x 25.4) R10 15.875 34.925 7.142 8.733 0.6250 x 1.375 x 0.2812 / 0.3438 — Emerson (mm = printed inch x 25.4) R12 19.05 41.275 7.938 11.113 0.7500 x 1.625 x 0.3125 / 0.4375 — Emerson (mm = printed inch x 25.4) R14 22.225 47.625 9.525 12.7 0.8750 x 1.875 x 0.3750 / 0.5000 — Emerson (mm = printed inch x 25.4) R16 25.4 50.8 9.525 12.7 1.0000 x 2.0000 x 0.3750 / 0.5000 — Emerson (mm = printed inch x 25.4) R18 28.575 53.975 9.525 12.7 1.1250 x 2.125 x 0.3750 / 0.5000 — Emerson (mm = printed inch x 25.4) R20 31.75 57.15 9.525 12.7 1.2500 x 2.250 x 0.3750 / 0.5000 — Emerson (mm = printed inch x 25.4) R22 34.925 63.5 11.113 14.288 1.3750 x 2.5000 x 0.4375 / 0.5625 — Emerson (mm = printed inch x 25.4) R24 38.1 66.675 11.113 14.288 1.5000 x 2.6250 x 0.4375 / 0.5625 — Emerson (mm = printed inch x 25.4) Files elsewhere (not hosted by Xem Studio; license as stated by the publisher): - NSK: Extra small and miniature ball bearings, inch series: d, D, B, r min (first 20 of 41 items: R09 to R2A) — web — Publisher's page; dimensions are facts — https://www.nsk.com/engineering/products/bearings/ball-bearings/deep-groove-ball-bearings/extra-small-ball-bearings-and-miniature-ball-bearings-inch-series.html - NSK: R166: d 4.762, D 9.525, B 3.175, r min 0.1 — web — Publisher's page; dimensions are facts — https://www.nsk.com/engineering/r166-esm-id.html - NSK: R144ZZ: d 3.175, D 6.35, B 2.779, r min 0.1 — web — Publisher's page; dimensions are facts — https://www.nsk.com/engineering/products/bearings/ball-bearings/deep-groove-ball-bearings/extra-small-ball-bearings-and-miniature-ball-bearings-inch-series/r144zz-esm-id.html - NSK: R188ZZ: d 6.35, D 12.7, B 4.762, r min 0.15; abutment db max 7.4, Db max 11.7, ra max 0.15 — web — Publisher's page; dimensions are facts — https://www.oss.nsk.com/r188zz-esm-id.html - Emerson Bearing: R-series miniature / instrumentation ball bearings R2 to R24: bore, OD, width (shielded / sealed and open) in inches — web — Publisher's page; dimensions are facts — https://products.emersonbearing.com/printitems/miniature-instrumentation-ball-bearings/r-series-miniature-instrumentation-ball-bearings?plpver=10 - TFL Bearing (SKF catalogue designations): Miniature deep groove ball bearings of the series R in inch sizes: d, D, B in mm and inches, R1-4 to R6 and WR — web — Publisher's page; dimensions are facts — https://tflbearing.com/?p=5029 - SKDIN (distributor): R188: 0.25 x 0.5 x 0.125 in (6.35 x 12.7 x 3.175 mm) — web — Publisher's page; dimensions are facts — https://www.skdin.com/products/productid-R188 - MBA (miniaturebearings.com.au): R188AZZMC3: ID 6.350, OD 12.700, width 4.762 mm — web — Publisher's page; dimensions are facts — https://miniaturebearings.com.au/products/6-350x12-7x4-762-bearings-r188azzmc3 Free files (CC BY 4.0, Xem Studio; STEP + STL, 22 parts): https://xemstudio.com/files/hardware/inch-ball-bearings-r-series-r188-r144-r166/index.json API: https://xemstudio.com/api/geometry?object=inch-ball-bearings-r-series-r188-r144-r166