What is the difference between M2, M3 and M4 styli?

Only the thread. M2 styli suit small probe heads and small balls (Ø0.3–2 mm), M3 sits in the middle and covers most CMM work, M4 is the heavier thread used on larger styli and CNC spindle probes. The thread must match the probe head; it cannot be adapted safely with an insert.

How small a ruby ball can I use?

Ø0.3 mm is the practical floor and Ø1.0 mm the practical everyday size. Below Ø1 mm, ball sphericity and stem-to-ball concentricity become the dominant error sources, so ask for the per-piece report rather than a batch report.

Which stem material should I pick?

Tungsten carbide for the smallest stem diameters and short lengths, ceramic where crash resistance and thermal stability matter more than minimum diameter, carbon fibre for long reaches over 100 mm where mass dominates.

Home / Products / M3 ruby styli

M3 ruby styli — Ø1 to Ø5 mm, carbide and ceramic

The middle thread, and the range that covers most CMM work. Twelve standard geometries in stock, from a Ø1.0 mm ball on a Ø0.8 mm carbide stem for small features, up to Ø5.0 mm on ceramic for general inspection.

M3Thread

Ø1–5Ball, mm

12Stock geometries

G10 / G5Ruby ball, ISO 3290

Standard M3 range

Codes are the factory part numbers. The last four digits map to the OEM number in the cross-reference column of the full catalogue. Every line ships with a batch calibration report; ask for a per-piece certificate on any line.

Code	Ball	Stem	Length	EWL	Typical use
BV-M3-21T-005R-7632	Ø0.5	Ø0.4 tungsten carbide	21	2.0	Micro features, thread roots
BV-M3-20T-01R-2442	Ø1.0	Ø0.7 tungsten carbide	20	12.5	Micro features, thread roots
BV-M3-30T-01R	Ø1.0	Ø0.8 tungsten carbide	30	22.5	Micro features, thread roots
BV-M3-40T-01R	Ø1.0	Ø0.8 tungsten carbide	40	32.5	Micro features, thread roots
BV-M3-50T-01R	Ø1.0	Ø0.8 tungsten carbide	50	42.5	Micro features, thread roots
BV-M3-21T-015R-0050	Ø1.5	Ø1.0 tungsten carbide	20	12.5	Small bores and slots
BV-M3-30T-015R-0051	Ø1.5	Ø1.0 tungsten carbide	30	22.5	Small bores and slots
BV-M3-20T-02R-3676	Ø2.0	Ø1.5 tungsten carbide	20	12.5	Small bores and slots
BV-M3-30T-02R-0052	Ø2.0	Ø1.5 tungsten carbide	30	22.8	Small bores and slots
BV-M3-40T-02R-0053	Ø2.0	Ø1.5 tungsten carbide	40	32.5	Small bores and slots
BV-M3-40C-02R-3646	Ø2.0	Ø1.5 ceramic	40	32.5	Small bores and slots
BV-M3-50T-02R	Ø2.0	Ø1.5 tungsten carbide	50	42.5	Small bores and slots
BV-M3-21T-025R-0054	Ø2.5	Ø1.5 tungsten carbide	20	12.5	Everyday inspection work
BV-M3-30T-025R-0055	Ø2.5	Ø1.5 tungsten carbide	30	22.5	Everyday inspection work
BV-M3-40T-025R-0056	Ø2.5	Ø1.5 tungsten carbide	40	32.5	Everyday inspection work
BV-M3-40C-025R-2545	Ø2.5	Ø2.0 ceramic	40	32.5	Everyday inspection work
BV-M3-20T-03R-7402	Ø3.0	Ø2.0 tungsten carbide	20	14.0	Everyday inspection work
BV-M3-30T-03R-0057	Ø3.0	Ø2.0 tungsten carbide	30	24.0	Everyday inspection work

Not on the list? M3 styli are the easiest range to build to drawing — stepped stems, tapered stems, mixed ball sizes, offset and star configurations. Send the drawing and get feasibility in 24 hours.

How to choose within the range

Three decisions, in this order.

Ball first. Pick the largest ball that still reaches the feature. Smaller balls measure tighter geometry but amplify surface finish into the result.
Then length. Use the shortest stylus that clears the part. Every 20 mm of extra length costs you measurable stiffness.
Then stem material. Carbide for minimum diameter, ceramic for crash tolerance and thermal stability, carbon fibre past 100 mm.

Rule of thumb used in most metrology labs: keep the ball diameter at least 3× the surface roughness you need to ignore, and keep the stem diameter at least 1/10 of the overall length.

Ask which one fits your part

M3 thread ruby ball styli with carbide and ceramic stems in various lengths

Specification, in numbers

Parameter	Standard	On request
Ball material	Ruby (synthetic corundum)	Silicon nitride, zirconia
Ball grade	Grade 10 to ISO 3290 (standard production)	Grade 5, imported balls, on request
Ball diameter tolerance	±2 µm	±1 µm with imported grade 5 balls
Sphericity	Per ISO 3290 grade 10 (≈0.25 µm)	Per grade 5 (≈0.13 µm)
Ball surface roughness	Typical for ruby (Ra ≤0.012 µm) — not measured per batch; sphericity governs	—
Stem straightness	≤5 µm over 100 mm	≤3 µm
Thread	M3, go/no-go gauged	M2, M4, M5, non-standard
Report	Batch report, ISO/IEC 17025 traceable	Per-piece certificate, USD 8–15
Stated tolerance	Grade per ISO 3290; actual measured value of each batch is printed in the shipped report	Report value governs, not this page
MOQ	1 pc	Volume pricing from 50 pcs

M3 stylus questions

Can I use an M3 stylus in an M4 head with an adaptor?

Physically yes, metrologically no. An adaptor adds a joint, and every joint adds both compliance and a datum you cannot verify. If the head is M4, buy M4 styli.

Do I need to recalibrate after changing a stylus?

Yes — requalify the stylus after any change, even same part number. The qualification defines the ball centre in machine coordinates, and that is what changes, not the stylus.

How many styli does a typical shop use per year?

A single CMM running one shift usually consumes 6–15 styli a year, mostly from crash damage rather than wear. Ruby is hard, but it is not indestructible against a rapid move into a vice.