Industrial MRO Reference Library · Technical Reference

Inch Bearings — R-Series & 1600 Series

R-series and 1600 series are inch-dimension ball bearings used in small motors, tools, rollers and equipment built to inch shafts. This sheet explains how the R number shows bore size, what the suffixes mean and how to measure for a replacement.

Ref MRO-0012ABMA 20

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Most ball bearings are metric. Inch-dimension deep groove ball bearings remain common in North American equipment. In the R-series (sometimes called instrument and miniature inch bearings in the small sizes), the number after "R" shows the bore in sixteenths of an inch. 1600 series bearings are another inch series with their own size scheme; the number does not decode directly to a fraction, so a size table is needed. Both use the same seal, shield and clearance suffixes as other ball bearings.

How to identify

Read the bearing face or box. An R-series bearing reads like R8-2RS or R6ZZ. Measure bore, outside diameter and width with a caliper in inches. If the bore is a clean fraction and the bearing is marked R, the number confirms the bore. For 1600 series and any R-series with a dash suffix, check the maker's table for OD and width. See bearing numbers decoded and shields vs seals ZZ, 2RS and variants.

R-series bore decoder

Number	Bore
R2	1/8 in
R3	3/16 in
R4	1/4 in
R6	3/8 in
R8	1/2 in
R10	5/8 in
R12	3/4 in
R14	7/8 in
R16	1 in

Rule: bore = number divided by 16, in inches. OD and width come from the maker's table.

Common suffixes

Suffix	Meaning
Z or ZZ	Metal shield on one or both sides
RS or 2RS	Rubber contact seal on one or both sides
C3	Internal clearance greater than normal
Dash and number (such as R2-6)	Size variant; OD or width differs from base size

Key points

Measure all three dimensions. Two bearings with the same bore can have different OD and width.
Some R-series sizes are made in open and shielded versions with different widths. Check before ordering.
Metric bearings close in size will not fit an inch shaft and housing correctly.
Flanged inch bearings carry an F in the part number on many brands. Flange size is in the maker's table.

Common mistakes

Swapping a metric bearing for an inch bearing because it "almost fits."
Reading 1600 series numbers as if they decode like R-series.
Ignoring the dash suffix and getting the wrong OD.

Governing standards: ABMA 20 (radial bearing tolerance classes); ABMA inch instrument bearing standards. Bearing maker dimension tables.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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