The impact microviscometer has been modified so that the ball can be rotated after an entrapment is formed. This rotation produces an extra circumferential shear stress which is much larger than the radial stress caused by the outward flow. Three fluids were studied by using this device. All displayed non-Newtonian behaviour at high shear stresses and appeared to be tending towards a limiting shear stress with increasing shear rate at pressures from 0.3 to 2 GPa. Data from one of the fluids (polyphenyl ether) were compared with results from a ball on plate traction test and a remarkable correlation was found. It seems reasonable to attribute the peak in the traction-slip curve to the ultimate shear stress that the lubricant can support.