Stylus guide · Part numbers · Materials · EWL

Every stylus part number is a sentence. Learn to read it once.

M4 STY D6R L50 EWL38.5 d4.5CE is not a code you have to look up. It is the geometry written out: M4 thread, straight stylus, Ø6 ruby ball, 50 mm overall, 38.5 mm effective reach, Ø4.5 ceramic stem. Read this page and you can specify a stylus without a catalogue — and check whether the one you were quoted is actually the one your part needs.

Decode a number Search 596 cross-references
Ruby ball CMM stylus mounted on a probe head
M2–M5Thread sizes
Ø0.3–Ø12Ball range, mm
4Stem materials
596Cross-references

Decoder

Paste a part number or a code string

Two kinds of input work: an OEM order number such as A-5000-3709, or the descriptive string printed next to it, such as M4 STY D6R L50 EWL38.5 d4.5CE. The lookup runs in your browser — nothing is sent anywhere.

Try A-5000-3709 A-5003-0054 M3 STR D2R L20 5BALL M4 EXT L100 d7 SS

WaitingType a number above.

The lookup covers the 596 part numbers we publish a cross-reference for. If your number is not there, it does not mean we cannot make it — send it and you will have a code, a price and a lead time within 24 hours.

Token by token

The six things a stylus code always tells you

TokenMeansValues you will seeWhy it matters
M2 … M5Thread at the mounting endM2 / M3 / M4 / M5M2 fits small and scanning heads, M4 and M5 the high-accuracy heads. Wrong thread, wrong probe family.
STY / STR / DSC / CYL / EXTType of bodySTY straight · STR star · DSC disc · CYL cylinder · EXT extensionDecides which features you can reach: bores, undercuts, deep walls.
D6RBall diameter and ball materialR ruby · Z zirconia · SN silicon nitride · TC tungsten carbideThe single biggest choice on this page. Material drives wear, not accuracy.
L50Overall length, ball centre to mounting face10 – 300 mmSets stiffness. Deflection grows with the cube of length.
EWL38.5Effective working lengthAlways less than LHow deep you can actually go before the stem fouls the part.
d4.5CEStem diameter and stem materialSS steel · TC carbide · CE ceramic · CF carbon fibreStiffness and mass. Deflection falls with the fourth power of diameter.

Note the two letters of the same shape: capital D is the ball, lower-case d is the stem. Most ordering mistakes live in that one character.

Length vs reach

Why a 50 mm stylus is not 50 mm of reach

A stylus is a cantilever, and the stem is thicker than the ball. On a Ø6 ball with a Ø4.5 stem you lose roughly 11 mm to the ball radius and the stem shoulder before the stem even touches anything.

Effective working length is measured from the ball centre to the point where the stem would contact the workpiece, along the part normal. Order by overall length and you will order a stylus that bottoms out on the shoulder of a bore. Order by EWL and you get what the drawing actually needs.

Two consequences worth remembering. First, a longer EWL on the same overall length means a thinner stem, which costs stiffness — the catalogue is full of stylus pairs that trade one for the other. Second, EWL only describes the straight approach. On an angled feature, clearance is governed by the ball-stem gap and by the part geometry, not by the number.

workpiece L overall to ball centre EWL stem shoulder is where the reach stops

Ball material

Ruby is the default. Three cases where it is the wrong answer.

Ball material is not about accuracy — the ball grade holds regardless of stem material. It is about what happens to the surface after ten thousand touches.

MaterialUse it forAvoid it onFailure mode if misapplied
Ruby Al₂O₃Steel, castings at low intensity, general inspection, everything you have not thought aboutContinuous scanning of aluminium; continuous scanning of cast ironAluminium transfers onto the ball; cast iron abrades it flat
Silicon nitride Si₃N₄Continuous scanning of aluminium and other sticky, soft alloysSteel — it wears markedly faster than ruby thereBall flats, then size drifts before you notice
Zirconia ZrO₂Continuous scanning of cast iron and other abrasive ironsVery hard thin coatings and some ceramics, where ruby is more predictableAccelerated wear against abrasive pearlitic surfaces
Tungsten carbide WCBalls below Ø1 mm, where a drilled ruby sphere is not practical; cylinder and disc tipsNothing in particular — but it is heavier than it looks and mass at the tip costs youProbe false triggers on fast moves if the tip mass is not accounted for

Rule of thumb: if the machine scans the same aluminium part all day, ask for silicon nitride. If it scans iron castings, ask for zirconia. If it touches a part once and moves on, ruby is right.

Stem material

Stiffness, mass and what breaks first

StemWhere it winsTrade-offTypical range
Stainless steelOne-piece bodies with no joint, best stiffness-to-mass at short lengthHeavy and whippy once you pass 30 mmL ≤ 30 mm, ball ≥ Ø2
Tungsten carbideSmall diameters, tiny balls, short stiff stemsDense; the tip mass starts triggering the probe on fast movesL ≤ 50 mm, stem Ø0.5–3
CeramicLong stems at ball sizes above Ø3, where it is nearly as stiff as steel at a third of the massBrittle — which is the point: it sacrifices itself instead of the probeL 30–150 mm
Carbon fibreLongest reaches, best damping, near-zero thermal expansionLower raw stiffness than ceramic at the same diameter; needs a bonded jointL ≥ 50 mm, up to 300+

A ceramic stem that breaks in a crash is cheaper than a probe head that bends in one. That is not a marketing line, it is the reason ceramic exists above 100 mm.

Selection

Three rules that resolve most arguments

01

Shortest that reaches

Deflection rises with the cube of length and falls with the fourth power of stem diameter. Double the length at the same diameter and you have eight times the bending. If a 50 mm stylus reaches the feature, a 100 mm stylus is not a safety margin — it is eight times the error.

02

Fewest joints

Every stylus-to-extension joint is another interface to seat, another source of bending, and another place for a chip to sit. Two 50 mm extensions are not equivalent to one 100 mm stylus.

03

Largest ball that fits

A bigger ball increases the ball-to-stem gap, so the stem fouls later and the effective reach goes up. It also averages surface roughness over a wider contact, which steadies the reading. Take the largest ball the feature allows, then size the stem to it.

Ball grade

Ball grade, and what actually goes on the purchase order

Sphericity is the one number no calibration offset can fix. Our standard production uses grade 10 balls to ISO 3290 (sphericity ≈0.25 µm, ball diameter ±2 µm) — the right choice for almost every CMM in a job shop. Imported grade 5 balls (sphericity ≈0.13 µm, ball diameter ±1 µm) are available on request for machines and contracts that specify them.

What most buyers never see is that the same nominal stylus is sold at different ball grades, and the grade rarely appears in the description. If the quote looks unusually cheap for a Ø2 ball, the grade is the first thing to ask about.

On a PO, three lines do more for you than any datasheet: the ball grade, a requirement for a per-batch calibration report traceable to an ISO/IEC 17025 accredited laboratory, and the EWL rather than only the overall length.

What to write on the order

  • Thread, ball Ø and ball grade
  • Overall length and EWL
  • Stem Ø and stem material — not just "ceramic"
  • Ball material when the part is aluminium or cast iron
  • Calibration report: batch or per piece, and to which standard
  • Acceptance: what you will measure on receipt, and to what tolerance
How our reports work

Questions we get every week

Straight answers

My machine is a Renishaw head. Do I have to buy Renishaw styli?

No. The interface is the thread and the seating face, and those are standardised. What you have to match is the geometry and the mass — a stylus that is 40% heavier than the original changes the probe's trigger behaviour. Match the mass, not just the drawing.

How much does a custom stylus cost?

Less than the downtime of waiting for one. Send the drawing with the four numbers above and you will have a price and a lead time within 24 hours; first article in three working days for most stepped and star configurations.

Can you make the star and disc bodies too?

Yes — star centres with 4 or 5 positions, disc styli for undercuts and grooves, cylinder styli for thin sheet, cranked bodies for turned parts. These are the ones that usually take six weeks from an OEM.

What if my OEM number is not in your list?

The published cross-reference is a subset, not the limit of what we make. Send the number or a photo of the stylus next to a rule, and the equivalent code comes back the same working day.

Do you publish prices?

No, and neither does anyone selling into this market honestly — stylus price depends on ball grade, stem material and quantity. Send a line list and you get a table back.

Is BEVY affiliated with Renishaw?

No. OEM part numbers appear on this site only to identify the part you already buy. BEVY Precision Metrology is an independent manufacturer; Renishaw and other brand names are the property of their respective owners and are used for reference only.

Next step

Send one part number. Get one answer within 24 hours.

Not a form, not a "we will revert". The equivalent code, the price, the lead time and the calibration option, in one reply.

Send a part number Search the cross-reference
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