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Lubricating oil and grease

A calculator that looks up the ISO VG kinematic viscosity range at 40 °C, oil types and VG for machine tools, how to choose hydraulic fluid, and NLGI grease grades.

Different brands of
grease:
please don't mix them!

÷ISO VG range

GradeMeasured kinematic viscosity at 40°C (optional)mm²/s

What is the ISO viscosity grade (ISO VG)?

A classification of industrial lubricating oils by kinematic viscosity at 40°C (mm²/s = cSt) (ISO 3448; in Japan, JIS K 2001 "Industrial lubricants — ISO viscosity classification"). The grade number is the midpoint of the 40°C kinematic viscosity, and each grade spans ±10% of the midpoint. Adjacent grades differ by a factor of about 1.5.^[1][2][3]

ISO VG kinematic viscosity at 40°C (midpoint and range, mm²/s)

Grade	Midpoint	Lower limit	Upper limit
VG 2	2.2	1.98	2.42
VG 3	3.2	2.88	3.52
VG 5	4.6	4.14	5.06
VG 7	6.8	6.12	7.48
VG 10	10	9	11
VG 15	15	13.5	16.5
VG 22	22	19.8	24.2
VG 32	32	28.8	35.2
VG 46	46	41.4	50.6
VG 68	68	61.2	74.8
VG 100	100	90	110
VG 150	150	135	165
VG 220	220	198	242
VG 320	320	288	352
VG 460	460	414	506
VG 680	680	612	748
VG 1000	1000	900	1100
VG 1500	1500	1350	1650

The range is the midpoint ±10%, so it can also be calculated (midpoint × 0.9–1.1). The text of ISO 3448 is paywalled, so the values were checked against the table published by Anton Paar. VG 2200 and 3200 were not checked this time.^[1](1 source, for reference)

Oil types and typical VG grades for machine tools (symbols are from the ISO classification of industrial lubricants)

Application	symbol	vg
Spindle, bearings, clutch	FC (rust and oxidation inhibited)	5, 10, 22, 32
Spindle, bearings (with anti-wear additive)	FD	2, 5, 10, 22, 32
Slideways (slideway oil)	G (oiliness, tackiness, anti-stick-slip)	32, 68, 100, 150, 220, 320
Hydraulic systems	HL (rust and oxidation inhibited)	32, 46, 68
Hydraulic systems (with anti-wear additive)	HM	15, 22, 32, 46, 68
Hydraulic and slideway combined	HM with anti-stick-slip properties added	32, 68
Enclosed gears (spur and bevel, medium load)	CKB	32, 68, 100, 150
Enclosed gears (worm, high load)	CKC (with extreme-pressure additive)	100, 150, 220, 320, 460, 680
Grease	XBCEA	Consistency numbers 00, 0, 1, 2, 3

From Idemitsu Kosan's oil selection table for machine tool oils (recommended product names omitted). In that table the combined hydraulic and slideway row is labeled HL, but its description says "HM with anti-stick-slip properties added"; the correct symbol could not be confirmed. For an actual machine, the oil specified by the machine manufacturer takes priority.^[4](1 source, for reference)

Choosing hydraulic fluid viscosity (when the machine manufacturer gives no specification)

Pump	Ambient 5–40°C	Ambient 40–80°C
Vane pump, 7 MPa or less	VG32	VG46、VG68
Vane pump, 7 MPa or more	VG46	VG68
Gear pump	VG32、VG46	VG100
Radial piston pump	VG32	VG68、VG100、VG150
Axial piston pump	VG68	VG68、VG100

Idemitsu Kosan's guideline, chosen by ambient temperature (5–40°C / 40–80°C) and pump type. If the machine manufacturer recommends a viscosity, use that.^[5](1 source, for reference)

Lubricants for ball screws and linear guides

In NSK's catalog, for ball screws a grease should be lithium-soap based with a base oil kinematic viscosity of 30–140 mm²/s (at 40°C), and an oil should be ISO VG32–100. It recommends lower viscosity for high-speed use where thermal displacement matters and at low temperatures, and higher viscosity for low speed, high temperature, oscillating motion, and heavy loads. For linear guides, intermittent oil feed uses VG68–220, and oil mist uses VG32–68, which atomizes easily.^[6](1 source, for reference)

Guide to inspecting and replenishing linear guide grease

NSK's guideline: inspect every 3–6 months (check for contamination and chips), replenish normally once a year, or every 3,000 km for conveyors and the like that exceed 3,000 km per year. Shorten or lengthen the interval according to inspection results.^[6](1 source, for reference)

Kinematic viscosity required for rolling bearings (at operating temperature)

bearing	Lower limit
Ball bearings, cylindrical roller bearings	13 mm²/s or more
Tapered roller bearings, spherical roller bearings	20 mm²/s or more
Spherical roller thrust bearings	32 mm²/s or more

These are values at the actual operating temperature, not at 40°C. The JTEKT catalog also has a table for choosing VG from operating temperature, dmn value ((outer diameter + bore) / 2 × rpm), and load (example: 0–60°C, dmn 300,000 or less, normal load: VG46).^[7](1 source, for reference)

Grease consistency and NLGI numbers

nlgi	penetration	Application
0	355〜385	For centralized greasing
1	310〜340	For centralized greasing, low temperature
2	265〜295	General purpose
3	220〜250	General purpose, high temperature
4	175〜205	Special applications

Consistency is the apparent hardness of a grease: ten times the depth in mm that a specified metal cone sinks under its own weight in 5 seconds (25°C, worked 60 strokes). The larger the number, the softer the grease. The table gives the ranges in the JTEKT catalog (grades 0–4 only; the ranges for 000, 00, 5, and 6 were not checked). Idemitsu Kosan's industrial greases are grades 00–3.^[7][8]

No. 2 for general use

JTEKT treats No. 2 as the general-purpose grade, and NSK says No. 2 consistency is best for grease in roller packs (linear guides).^[7][6]

Do not mix greases of different brands

If the thickener types differ, the structure can break down, and even with the same type, differences in additives can cause harm. If unavoidable, choose one with the same thickener and test it beforehand.^[7][6]

📚Sources

Items without a mark are those on which two or more materials from different publishers agree. For product values, each manufacturer's documentation takes precedence. The text is summarized in Kezuriba's own words.