Helper springs are usually the 4lbs type that have no influence on the actual ride/handing of the car as they only provide some means of keeping the main spring seated.
As the ride height of the car is lowered, by reducing pre-load on the main spring, there becomes a point you need helper springs to keep the main spring in check (seated) as the suspension extends completely.
2.25" helpers and joiners here http://www.dfaulknersprings.co.uk/helpers.htm
Eibach Springs - Understanding Spring Codes
Eibach ERS 'imperial' springs are coded as:
So that would be a 6 inch long, 2.25" diamater and 125 lb/in spring.