Ceramic or carbon fibre for long reach?

Carbon fibre is lighter and damps vibration better, so it is the usual choice above 150 mm. Ceramic is stiffer per unit diameter and more stable thermally, so it wins between 100 and 150 mm and wherever the stem diameter has to stay small.

How much does a long stylus deflect?

Deflection scales with the cube of length and inversely with the fourth power of stem diameter. Doubling the length increases deflection eight times for the same stem. That is why long reach styli use larger stem diameters or a lower-density material rather than a thinner stem.

Can a long stylus be used on a manual machine?

Yes, but only with a rigid stand and a slow approach. Long styli amplify both probe and operator error, and a crash at 200 mm length usually destroys the stylus and can damage the head.

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Long reach styli — 100 to 300 mm without losing the tolerance

Reach is easy to add and hard to keep. Past 100 mm, deflection stops being a footnote and starts being your uncertainty budget. These are the geometries and materials that keep a long stylus measurable.

100–300Overall length, mm

CeramicStandard stem

Carb.fibreAbove 150 mm

G10 / G5Ruby ball, ISO 3290

Why length is expensive

A stylus is a cantilever. Its stiffness falls with the cube of length.

Overall length	Relative deflection	Practical consequence
50 mm	1×	Negligible against most tolerances
100 mm	8×	Qualify carefully; avoid fast moves
150 mm	27×	Carbon fibre becomes the default
200 mm	64×	Part handling and clamping dominate error
300 mm	216×	Accept wider uncertainty or redesign the fixturing

Indicative values for the same stem diameter and material. The practical lesson: if you need 200 mm of reach, the answer is usually a bigger stem diameter or a lighter material, not a thinner stylus.

Long reach CMM stylus with 200 mm ceramic stem and ruby ball

Standard long reach geometries

Extensions and one-piece long styli are not interchangeable. A joint at 100 mm adds compliance you cannot qualify away — one-piece is the right answer above 150 mm.

Code	Thread	Ball	Stem	Length	Material
BV-M4-75C-05R-0236	M4	Ø5.0	Ø4.0	75	Ceramic
BV-M4-75C-06R-2764	M4	Ø6.0	Ø4.5	75	Ceramic
BV-M4-75C-08R-4802	M4	Ø8.0	Ø4.5	75	Ceramic
BV-M4-100C-05R-9761	M4	Ø5.0	Ø4.0	100	Ceramic
BV-M4-100C-06R-3712	M4	Ø6.0	Ø4.5	100	Ceramic
BV-M4-100F-06-6510	M4	Ø6.0	Ø4.5	100	Carbon fibre
BV-M4-100F-06R-1358	M4	Ø6.0	Ø4.5	100	Carbon fibre
BV-M4-100C-08R-7796	M4	Ø8.0	Ø4.5	100	Ceramic
BV-M4-150C-06R-8156	M4	Ø6.0	Ø4.5	150	Ceramic
BV-M4-100C-07E-7727	M4	—	Ø7.0	100	Ceramic extension

Above 150 mm most buyers should be asking a different question: can the fixture be changed instead? It is usually cheaper than accepting a wider uncertainty for the next five years.

What we can hold on a long part

Parameter	Standard	Notes
Stem straightness	≤5 µm over 100 mm	≤3 µm on request
Ball position, axial	±15 µm	Measured on the assembled part
Ball position, radial	≤10 µm runout	Determines the effective radius you must enter
Thread squareness	≤5 µm	Gauged, reported
Mass	Reported per part	Matters above 150 mm for head limits

Long styli are quoted against a drawing, not from a list, because the usable geometry depends on your fixture clearance. Send the part and the fixture photo; the answer is usually obvious in one look.

Long reach questions

Can I stack extensions to get 300 mm?

You can, and you will measure something. Two joints at 300 mm add roughly 10–20 µm of unpredictable compliance depending on torque. If the reach is permanent, buy a one-piece part.

Does mass matter to the probe head?

Yes. Probe heads have a rated stylus mass, and exceeding it causes missed triggers or false triggers. A 300 mm carbon fibre stylus is around 30–40 g — ask before you exceed the head's limit.

Will a ceramic stem survive a crash?

It breaks instead of bending, which protects the head. That is the intended failure mode, and it is why ceramic is preferred on manual machines. Keep a spare.

Send the part and the fixture. Get the reach that works.

Drawings, a photo with a ruler, or just the depths and clearances. Answer in 24 hours, first article in 72.

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