51168-M bearing: complete specifications & equivalents

Specification table

Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018)) · extracted 2026-09-28

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 51168-M model number is decoded

51168 M is SKF's 340 mm-bore single-direction thrust ball bearing in the 51100 series to the ISO 104 dimension plan, with a flat housing seating surface, measuring 340×420×64 mm. The separable set comprises a shaft washer (ground bore, tight fit on the shaft), a loose-bore housing washer and one ball-cage assembly, reacting axial force in one direction and carrying no radial load. in the 51xxx designation the first 1 marks a single-direction bearing with a flat housing seating surface; the third digit 1–4 grades the dimension series from the light 511 section through the heavy 514 section. the final two digits 68 encode the bore as 340 mm (code 68 × 5), the standard SKF bore-code rule shared with radial bearings. suffix M identifies a one-piece machined brass cage, ball-centred: the large-size and heavy-section option for higher speeds, shock loads and thin-film lubrication where a pressed cage would distort. Envelope 340×420×64 mm (13.386×16.535×2.52 in), 40.0 mm radial section, C 377 kN, C0 1960 kN, Pu 37.5 kN. reference speed 800 r/min (thermal) and limiting speed 1,100 r/min (mechanical), catalogue mass 20500 g. Preload at the mechanical ceiling: repeating Fam ≈ A·(n·dm/1000)² with factor A 20 at the 1,100 r/min limiting speed raises the required axial preload to about 3494.5 kN; the reference-speed value 1848.3 kN is the thermal design point. At the printed limiting speed of 1,100 r/min the mean pitch diameter dm ≈ 380.0 mm implies a dn value around 418k mm·r/min; the 800 r/min reference speed is the thermal-planning value under catalogue load. Speed band width for this size is 300 r/min between reference and limiting (1.38× ratio); lubrication, preload and heat removal decide where inside that band 51168 M can actually run. Light-load floor: Pu = 37.5 kN is the equivalent-load threshold below which the SKF adjusted-life equation credits very long life for 51168 M; the number is 10 % of the 377 kN dynamic rating. Static-first selection data: 1960 kN C0 spread across the 64 mm stack gives 30.6 kN of static rating per height millimetre, and the 20500 g mass/C0 ratio is about 10 g per static kN — crane-hook and screw positions are normally sized on these two figures. Machined-cage order-number note: the M brass cage is a one-piece ball-centred window cage, chosen at the heavy end of the section for speed and shock duty; it is heavier and stiffer than the pressed-steel execution of the smaller sizes and tolerates interrupted lubrication far better, which is why the catalogue restricts the M suffix to the large bores. At 20500 g the machined brass cage represents a meaningful fraction of total mass; balancing checks on high-speed 340 mm vertical shafts should use the actual M-execution weight, not the lighter pressed-cage catalogue value.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• Keep the applied thrust above Fam ≈ A·(n·dm/1000)² with the printed factor A 20; for 51168 M a spring preload or the rotor weight is part of the selection at light load and high speed, because unloaded balls skid rather than roll.
• The three components are separable and interchangeable within the ISO 104 size, but keep this bearing's parts together in service and never combine washers from different manufacturers or a worn washer with a new ball set.
• The third digit grades the section: 511 light, then 512, 513 and 514 progressively taller and heavier at the same bore — select from 377/1960 kN and the available 420 mm OD, never substitute a lighter series for a heavier one without rechecking C and C0.
• The 51168 M is a pure axial bearing: it must never be subjected to radial load — any radial force on the 340 mm shaft has to be carried by a radial bearing mounted alongside it.
• Ordering discipline for 51168: the catalogue page quotes 51168 M and its 377/1960 kN ratings as one exact article; bare-number substitutions from another series or brand need a fresh dimension and rating check, not a like-for-like assumption.