If you have grown yardlong beans, they are generally at their prime when pencil width or less. The pods of Sierra Madre are exceptionally slow to develop seed, so they can grow larger & still be fiber-free. The pod in the photo is the same width as the Emerite snap beans I am currently harvesting. I have recommended this as a replacement for snap beans for those in hot climates, and those I've sent seed have reported good results.
This year, I am growing two other yardlong/edible pod cowpeas. Taiwan Black is a pole yardlong with narrow, pale green pods & black seeds. It is much narrower than Sierra Madre at harvest stage, and has a delicate texture. It also has the second shortest DTM & second highest yield of my pole yardlongs.
Bush Sitao BS-3 is a variety bred in the Philippines for edible pods ("sitao" is Filipino for "long bean"). It has a sprawling bush habit, and light green, very straight 8-9" pods with firm texture. I will be testing them as dilly beans this year.
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Bush Sitao BS-3 (in 2012)
Both of those are located in my rural garden, and were subjected to heavy weed pressure until recently (the Bush Sitao was only weeded two days ago). The yardlongs/cowpeas in that garden tolerated the weeds better than anything else there; and while behind schedule, are healthy & blooming now.