3309-DMA bearing: complete specifications & equivalents

Specification table

Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018)) · extracted 2026-09-27

Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018)); SKF® and SKF Explorer® are trademarks of AB SKF, used here for identification only — mpnbase is not an authorized SKF distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at skf.com.

Cross references & equivalents

Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.

How the 3309-DMA model number is decoded

3309 DMA is SKF's 45 mm-bore double-row angular-contact ball bearing of the 3300 series — two ball rows back-to-back for two-direction axial location in one unit, 45×100×39.7 mm. A on a double-row bearing means no filling slots, so both rows carry their full ball complement in both directions. D marks a two-piece (split) inner ring that simplifies mounting of the heavy 33-series section. DMA pairs the split inner ring with a machined brass outer-ring-centred MA cage. Envelope 45×100×39.7 mm (1.772×3.937×1.563 in), 27.5 mm radial section height, C 79.3 kN, C0 69.5 kN, Pu 3 kN.reference speed 7,500 r/min (thermal) and limiting speed 6,300 r/min (mechanical), catalogue mass 1650 g. Selection figures for 3309 DMA: the static-to-dynamic ratio C0/C is 0.88, Pu 3 kN is about 4 % of C, and catalogue mass works out to roughly 37 g per millimetre of bore. Envelope economics: the 39.7 mm width over a 27.5 mm section yields 1.44 mm of ring width per section millimetre, and the bearing weighs 1650 g for 79.3 kN of dynamic capacity — about 21 g per rated kN. Speed-ratio note for this exact unit: the reference speed is 7,500 r/min against a 6,300 r/min limiting speed, i.e. a reference-to-limit ratio of 1.19. Split-ring execution note: DMA combines the two-piece inner ring (used to simplify mounting of the wide 33-series section) with a machined brass cage guided on the outer ring (MA rather than ball-centred M); outer-ring guidance steadies the cage in the heavy section at the cost of a different lubrication requirement at the guide land.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• Catalogue ratings of 79.3/69.5 kN apply to the DMA execution; the D and DNRCBM two-piece-ring executions carry their own figures on their own pages.
• The double-row 3309 takes thrust in both directions by itself — that is the reason to choose it over two single-row bearings: one housing bore, one fit, built-in set geometry.
• Interference goes on the rotating ring (about k5 at 45 mm bore); the wide 39.7 mm ring is sensitive to tilted seats, so check squareness before clamping.
• Compared with a single-row pair of the same bore, the double-row 3309 occupies less axial space but offers less freedom to adjust preload — do not substitute without re-checking the arrangement.
• The D executions have a two-piece inner ring: mount both halves square to each other, never press on the outer ring, and keep the split faces clean during fitting.
• Catalogue ratings are SKF PUB BU/P1 17000 figures for 3309 DMA as the double d ma execution; the other order numbers of the 3309 size are different products and may carry different ratings — always quote the full designation when purchasing.