APG O87, an ester based fluid with a saturation of 250 Gauss and a viscosity of 750 centipoise. Manufactured by Ferrotec USA .
Other available formulations, contact us for details:
CDF 2250 (Ester based): 220 Gauss, 500 cP
APG 1134 (Hydrocarbon): 220 Gauss, 1000 cP
These are the specific fluids used by major drive unit manufacturers.
Beware: some unscrupulous sellers are offering the cheap, commonly available science project type ferrofluid as an audio product. This results in an overdamped output and can soften drive unit adhesive - always double check the origin and the specification.
Ferrofluid is a cooling / damping compound used in the magnetic gap of many tweeters to increase power handling and smooth out the frequency response; it has a tendency to thicken with age, gradually reducing tweeter output to zero. Many old tweeters from the 1980s/90s can be restored to perfect working order by carefully dismantling and cleaning out the old coagulated fluid then replacing with fresh.
This refill kit comprises a high accuracy syringe pre-filled with Ferrofluid specifically formulated for high fidelity tweeter application. There is sufficient in the syringe for 2 tweeters & a micro applicator nozzle is supplied.