Are the parts together or are they separated?
Are we talking strictly 2-D measurements from one aspect, e.g., is the projected diameter in one orientation sufficient and we don't need to look for out-of-roundness?
One obvious solution is a vision system, which could potentially process 20 pcs/sec, depending on how pcs can be in the field of view of the imager. Assuming 1/4 mil resolution, you'll need something with at least 500 pixels on the long dimension, while the narrow dimension only occupies 80 pixels. So you could have up to 4 or 5 pcs in a 512x512 pixel imager field of view.
TTFN