2x8 douglas fir for all the stringers. The original outside stringers were only plywood which seemed pretty flimsy so decided to use the 2x since that is were everyone steps on and off the boat from the dock. I did have to call around and found one lumber yard in my area that could order in the 2x8 x 16' so it was a little pricey but we are happy with how it is all turning out.