3780-3720 bearing: complete specifications & equivalents

Specification table

Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.2 inch single-row TRB) · extracted 2026-09-28

Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018), ch. 8.2 inch single-row TRB); 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 3780-3720 model number is decoded

Dimensional interchange map: within the 37800 series at 50.8 mm bore, the 93.264 mm OD and 30.162 mm width are fixed by the ISO 355 plan, so any same-code bearing from another brand shares the mounting envelope; the 21.2 mm section height distinguishes this family from a 302 or 322 of the same bore, and the 870 g mass is the minimum—sealed or snap-ring executions add rotating weight above that catalogue baseline. A single-row inch tapered bearing is quoted as a cone/cup pair because the boundary dimensions belong to the combination, not to either half alone: in 3780 the 3780 cone contributes the 50.8 mm bore and roller set, the 3720 cup contributes the 93.264 mm OD raceway, and the assembled 30.162 mm width is the catalogue value.For a 50.8 mm shaft carrying combined load, SKF lists 3780 under catalogue execution SKF 3780/3720: one open single-row tapered roller bearing in the inch 3700-series.Reading the designation: 3780 follows the Timken-style inch convention — the cone (inner ring with rollers) and cup (outer ring) are quoted as a pair separated by a slash, and the 3700-series code identifies the dimensional series. The 50.8 mm bore, 93.264 mm OD and 30.162 mm width are the metric equivalents of the inch boundary dimensions. SKF lists the plain number as the basic execution; letter suffixes such as B denote a steeper contact angle and are different order numbers. The 21.2 mm radial section height ((93.264−50.8)/2) and 870 g catalogue mass frame a 50.8 mm bore bearing rated at 134 kN C — roughly 2.64 kN of dynamic capacity per millimetre of bore before application factors. A single 3780 locates the shaft in one axial direction only; mount it against a second bearing in O (back-to-back) or X (face-to-face) arrangement, and set the running clearance by the mounting procedure — not by feel.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• On this 50.8 mm bore, interference and temperature rise consume clearance inside a preloaded pair; calculate the residual clearance after mounting and at operating temperature — an over-tight 3780 pair heats, loses setting control and smears the roller-rib contact.
• The 320 series at 50.8 mm bore (93.264×30.162 mm) is the low-friction, higher-speed section; it carries less thrust than a 302 of the same bore, so verify the axial load share before swapping.
• O (back-to-back) pairs are stiffer against moments, X (face-to-face) pairs tolerate misalignment and thermal growth better; choosing the arrangement from the 2D drawing rather than the actual shaft thermal expansion is a common 3780 mounting error.
• At the 134 kN rating of 3780, preload class changes stiffness by tens of percent but also heat generation; select light preload for the 7,000 r/min speed end and heavier preload only where moment stiffness dominates.
• The 3780 shares its ISO 355 envelope with other tapered bearings of the same code but is not a drop-in replacement for a ball bearing: it cannot run effectively under pure radial load without a minimum axial load, and a deep-groove bearing cannot replace its combined-load duty.
• The 134/146 kN ratings are SKF catalogue 17000 values for the basic execution; SKF can revise internal geometry without changing the order number, so keep the catalogue version (PUB BU/P1 17000/1 EN, 2018) with the specification and re-verify for critical drives.
• SKF lists several executions of 3780 (basic, B steeper angle, Q/J2 clearance variants); they are not interchangeable order numbers — quote the full SKF 3780/3720 designation when purchasing and match the execution to the mounting arrangement.