Stainless steel shafts: choosing the grade, the fit tolerance and the straightness limit

October 26, 2026

A shaft looks like the simplest machined part. It is a round bar with a few steps, a keyway and perhaps a thread. In stainless it is also one of the parts most often rejected for reasons that have nothing to do with the cut: the bar was not straight, the heat treatment bent it, the grade galled against its bushing or the diameter tolerance was tighter than the finishing process could hold at a sensible price.

This guide covers the three decisions that matter on a stainless shaft: which grade, which tolerances and how straight. It focuses on what a buyer writes on the drawing and the quote request.

Grade: start with the environment

Grade	Condition	Yield, typical	Machinability	Corrosion	Good for
303	Annealed	240 MPa	78	Moderate, no chlorides	Light duty, dry indoor shafts
304	Annealed	205 to 250 MPa	45	Good in mild service	General, wet but not saline
316L	Annealed	170 to 250 MPa	36	Better in chlorides	Wet, washdown and food
416	Hardened and tempered	550 to 900 MPa	85	Poor, dry only	Strong, hard, dry shafts
17-4 PH	H1025	about 1000 MPa	50	Moderate	High strength with some corrosion resistance
2205 duplex	Annealed	450 MPa	30	Strong in chlorides	Pump and marine shafts
Nitronic 60	Annealed	about 400 MPa	35	Like 304, with galling resistance	Wear and galling duty

Machinability and PREN values follow the site grade reference. Yield values are typical published figures and vary by condition and size, so confirm on the certificate. See the stainless grades reference for the full set.

Reading the table:

• Dry, light load, low cost. 303 or 416, but not where chloride is present.
• Wet or washdown. 316L is the usual choice, despite low strength. If strength is short, 17-4 PH in a higher H condition or duplex.
• Marine or chloride, heavy load. 2205 duplex gives strength and corrosion resistance together. See the 2205 guide and the marine stainless guide.
• Sliding fits and threads. Galling matters as much as strength. Nitronic 60 or a hardened surface helps. See the Nitronic 60 guide.
• Hard, wear-resistant surface. 416 or 420 hardened, or a nitrided surface where allowed. See the martensitic stainless guide.

Free-machining grades (303, 416) cut fast but should stay out of wet service and food contact.

Tolerances: use the ISO 286 system

Shaft tolerances are written as a letter and a number. The lowercase letter sets the position of the tolerance band, and the number sets its width. For shafts, h means the upper limit is the nominal size, and g sits slightly below nominal for a running clearance.

Example values for a nominal diameter between 18 and 30 mm (the 20 mm case), from ISO 286:

Class	Upper limit	Lower limit	Band	Typical use
h6	0	−13 µm	13 µm	Bearing seats, precision fits
h7	0	−21 µm	21 µm	General fits, seals
h8	0	−33 µm	33 µm	Looser fits
h9	0	−52 µm	52 µm	Non-critical turned diameters
g6	−7 µm	−20 µm	13 µm	Sliding or running clearance
k6	+15 µm	+2 µm	13 µm	Light interference, locating

Numeric values change with the diameter range. Check ISO 286-1 for the real size, since a 6 mm and a 60 mm shaft have different bands for the same class.

Cost follows tolerance. A turned shaft typically holds h8 to h9 without extra effort. h7 on stainless usually needs a careful finishing cut or grinding. h6 normally needs grinding or fine turning on a rigid machine. The tolerance guide puts numbers on each step. Use tight classes only where a bearing, seal or interference fit needs them, and leave the rest to a general note such as ISO 2768-m.

Also state:

• Surface finish on seal and bearing surfaces, for example Ra 0.4 µm for a lip seal. See the surface finish guide.
• Runout or concentricity between bearing seats, for example 0.02 mm TIR, as a GD&T callout.
• Cylindricity or roundness, if needed for sealing.

Straightness: the quiet source of rejection

Straightness is the deviation of the shaft axis from a straight line. Drawings often skip it, and then the shaft arrives bent.

Where the bend comes from:

1. Bar as supplied. Mill bar has a straightness tolerance, usually expressed per length. Cold drawn and ground bar is straighter than hot finished bar, but both can carry residual stress.
2. Machining stress release. Removing material from one side relieves residual stress and the bar bows. Heavy cuts and asymmetric features such as keyways and flats make it worse.
3. Heat treatment. Hardening and ageing distort slender parts. A 17-4 PH or 416 shaft hardened after machining usually needs straightening or finish grinding afterward.
4. Work hardening. Cutting hardens the surface of austenitic stainless and can add stress. See the work hardening guide.

Typical practical figures, which vary by diameter and length:

Shaft	Length to diameter	Typical straightness after turning	Cost to tighten
Short, stocky	under 5:1	0.02 to 0.05 mm over length	Low
Medium	5:1 to 10:1	0.05 to 0.1 mm over length	Medium
Long, slender	over 10:1	0.1 mm per 300 mm and worse	High, needs steady rest, straightening, grinding

Values are typical planning ranges. If straightness matters, write it as a limit over a length, for example 0.05 mm over 300 mm, and say how it is measured, for example between centres with a dial indicator. Without a stated limit the shop will choose its own, and the shaft that is straight enough for the shop may wobble in a bearing.

Slender shafts need support on the machine, such as a steady rest, centres and reduced cutting depth. They may also need a stress relief step before finishing. The standard stress relief for austenitic stainless risks sensitisation if done at the wrong temperature, so do not assume a stress relief temperature. Ask the shop or specify the cycle.

Need a quote for this part? Get a quote for your stainless parts

Process route for precision shafts

A typical sequence for a tight, straight shaft:

1. Cut bar with extra length for centres.
2. Rough turn, leaving 0.5 to 1 mm on diameter.
3. Stress relieve or straighten if the grade allows.
4. Heat treat if the grade is hardenable.
5. Finish turn or centreless grind to size.
6. Cut keyways, flats, threads and cross holes.
7. Deburr, passivate, clean and inspect.

The finishing step sets final size and roughness. Each additional step adds cost, so pick the least number of steps that meets the drawing.

Threads, keyways and ends

• Threads on stainless shafts gall. Use a looser class and food-grade anti-seize where allowed. See the threading guide.
• Keyways release stress and cause bending. Cut them before the final finishing pass if possible, and state the tolerance on the width.
• Centre holes are the datum for turning and grinding. If you do not want them on the finished shaft, say so.
• Chamfers and radii at shoulders affect fatigue life. A sharp internal corner at a shoulder is a stress raiser. State a radius.

What to write on the drawing

• Grade, UNS number, bar standard and condition. See the bar specification guide.
• Tolerance class on each critical diameter, with the finish.
• Straightness limit over length and the measurement method.
• Runout between bearing seats.
• Hardness range if the grade is hardened.
• Passivation standard and cleaning.
• Certificate level.

The RFQ checklist lists the rest of the information a shop needs.

Inspection of a shaft

A shaft is easy to measure in principle and often measured badly in practice. A few checks give a reliable answer.

• Diameter with a micrometer or a snap gauge at two or three positions along each journal and at two angles, which shows size, taper and ovality. A single reading at one point hides taper.
• Runout with the shaft supported on its centres or on V blocks at the bearing seats, and a dial indicator on the other diameters. Total indicator reading shows bend and eccentricity together.
• Straightness by rolling the shaft on a surface plate or by measuring runout along its length. Report it as a value over a length.
• Surface finish with a profilometer on seal and bearing surfaces.
• Hardness at a defined location for hardened grades.
• Thread and keyway with go and no-go gauges.

For critical shafts, request a report that lists each of these with the measured values. The CMM report guide explains how to read dimensional results. Note that a CMM is not the best tool for long, slender shafts, where support conditions affect the reading, and a measurement between centres is more representative of how the shaft runs.

Shipping and handling

Shafts bend in transit. Pack long shafts supported along their length, in tubes or in boxes with spacers, not stacked loosely. Protect polished journals with a clean wrap or sleeve and keep them off carbon steel. For long shafts, mark which end goes up in storage so the shaft does not sag under its own weight. A shaft that arrives straight and ships back bent after a rough trip creates an argument about the cause, so agree packaging at the order stage.

Checklist before you request a quote

• Grade chosen for the environment first, then strength.
• Tolerances limited to bearing, seal and fit diameters.
• Straightness stated, not assumed.
• Finishing route agreed: turning, grinding or both.
• Heat treatment and distortion plan stated for hardened grades.
• Galling plan for threads and sliding fits.

Send the drawing through the RFQ form. We send one itemised quote within 24 business hours and place the work with partner shops that turn and grind stainless shafts. We own no machines.

Frequently asked questions

Figures in this guide are published specification limits or published typical values for the alloy, not measurements of any part. Machinability is rated against free-machining carbon steel B1112 at 100 and PREN is chromium plus 3.3 times molybdenum plus 16 times nitrogen. The conventions are set out in thereference section and the editorial standards.

Keep reading

• Stainless steel parts for cryogenic service: 304L against 316L, what impact tests do and do not prove and what to put on the order
• 316L for hydrogen service: why nickel content, cold work and heat history matter more than the grade name