2.5 g per hr or per sec .

Simple enough use a1inch or smaller diametre , 6 to 12 inches long square tread bolt conect it to a motor , fit it inside a pipe ,make a hole in the pipe , attach a funnel to the hole , you have your screw feeder. No calculations needed.

control the speed of the motor to meet your needs. (you can use a variable speed drill motor if you find one) otherwise use a variac.

Marco ■

You could also use a wood cutting bit. (as is used with a brace & bit for making holes in wood)

This type of "auger" comes in a lot of different diameters and has more open area than an acme thread screw which should help to avoid plugging. ■

Marco & JD have certainly ripped the mystique out of dosing with screw conveyors. I bet there are some high tech outfits out there who have just got screwed themselves. Thanks very much: I'm off to B&Q right away. ■