BEARINGDEX
Deep groove ball, miniature

638 bearing

8 mm bore, 28 mm outside diameter, 9 mm width (0.315 × 1.1024 × 0.3543 in).

Cross-reference 638Decode a full part number

Dimensions

mminch
Bore d80.3150
Outside diameter D281.1024
Width B90.3543

Quick numbers

Pitch diameter dm18.0 mm
Section height (D − d)/210.0 mm
n·dm at 1,800 rpm32,400
n·dm at 3,600 rpm64,800

Compare against the maker's limiting speed. Speed calculator · L10 life

What the number means

6Deep groove ball
3Diameter series 3: medium
8Single digit: bore is 8 mm, written directly

How each brand writes it

Same bearing, every maker's notation
VersionSKFFAGNSKNTNKoyoNACHI
Open638638638638638638
Shields both sides638-2Z638-2ZR638ZZ638ZZ638ZZ638ZZE
Contact seals both sides638-2RSH638-2RSR638DDU638LLU638-2RS638-2NSE
Contact seals both sides, C3638-2RSH/C3638-2RSR-C3638DDUC3638LLUC3638-2RSC3638-2NSE C3 Verify
Non-contact seals both sides638-2RSL638-2BRS Verify638VV638LLB638-2RU Verify638-2NKE Verify
Shields both sides, C3638-2Z/C3638-2ZR-C3638ZZC3638ZZC3638ZZC3638ZZE C3 Verify