The industry standard and the optimum stylus ball material for a
vast majority of measurement applications, ruby is one of the
hardest known materials. Synthetic ruby is 99% pure aluminium oxide
which is grown into crystals (or "boules") at 2000 °C using the
The boules are then cut and gradually machined into a highly
spherical form. Ruby balls are exceptionally smooth on the surface,
have great compressive strength and a high resistance to mechanical
Very few applications exists where ruby is not the preferred ball
material, however there are two applications where balls
manufactured from other materials are recommended.
The first is for heavy duty scanning applications on aluminium.
Because the materials attract, a phenomenon known as 'adhesive wear'
can occur, which involves build up of aluminium from the surface
onto the ball. A better ball material for such applications is
The second is in heavy duty scanning applications on cast iron.
Interaction between the two materials can result in 'abrasive wear'
of the ruby ball surface. For such applications, Zirconia balls are
Silicon nitride possesses many similar properties to ruby. It is a
very hard and wear-resistant ceramic which can be machined into high
precision spheres. It can also be polished to an extremely smooth
Silicon nitride does not have an attraction to aluminium and so does
not exhibit the adhesive wear seen with ruby in similar
applications. However, silicon nitride does show significant
abrasive wear characteristics when scanning on steel surfaces and so
its applications are best confined to aluminium.
Zirconia is a particularly tough ceramic material with hardness and
wear characteristics approaching those of ruby. Its surface
properties make it an ideal material for aggressive scanning
applications on cast iron components.
Stylus stems manufactured from non-magnetic stainless steel are used
widely for styli with ball/tip diameters of 2 mm or greater and with
lengths up to 30 mm. Within this range, one-piece steel stems offer
the optimum stiffness to weight ratio, giving adequate ball/stem
clearance without compromising stiffness with a joint between the
stem and threaded body.
Tungsten carbide stems are best used for maximising stiffness with
either small stem diameters required for ball diameters of 1 mm and
below, or lengths up to 50 mm. Beyond this, weight can become a
problem and stiffness is lost due to deflection at the stem to body
For ball diameters greater than 3 mm, and lengths over 30 mm,
ceramic stems offer stiffness comparable to steel but are
significantly lighter than tungsten carbide. Ceramic stemmed styli
can also offer additional crash protection to your probe as the stem
will shatter in a collision.
Carbon fibre styli weigh around 20% less than tungsten carbide
styli, making it a suitable material for long styli. Its thermal
stability is also advantageous, particularly with very long styli,
which makes it suitable for use in a production environment.
This is a very light material so is ideally suited for extensions,
but only in a stable air-conditioned environment due to thermal
Titanium is thermally stable compared to aluminium, has good
flexural rigidity and is also very light. These characteristics make
it very suitable for long extensions.