My thumb is on the main pin of my coupler. It is 14" wide. I use an adapter to couple onto loader backhoe buckets. My 12" bucket is from a 580SL. With the coupler, it is 38" to the teeth, so i can drag my pin thru the top of the trench and get 42" deep with the top slightly wider then 14".
This is mostly clay dirt that was hauled in to build it up. There are no rocks, but it has been dry for 3 weeks, so it is hard and soft, with clods that will dig like rocks. I'm hoping it will rain before i have to dig there.
I'm in Iowa and digging a foundation for a garage. We have to be 4' in the ground with the footing and then they are pouring a knee wall that the garage will be framed on.