There are many different varieties.
They are picked when the beans are young and very slender (less than 1/4 inch / 1/2 cm thick) and 5 to 7 inches (13 to 18 cm) long.
Older varieties will develop strings if you let them grow too much past that size, so you have to harvest them often, around every other day.
The beans inside are dark.
Some people rave about the taste; others say they can’t really taste any difference between Filet Beans and normal green beans.
Filet Beans generally don’t can or freeze well.