Two flat jaws would be ideal for the irregular length of the wood, (although straight edged).
I've used "normal" 50mm jaws with x2 taken out but with poor results as they have a knack of flying out.
I probably should have said originally that as the stock is flat looking for flat jaws.
If there is such a thing for a wood lathe.
Surely if you put flat timber inside flat jaws and you only have two jaws, there is an inherent risk of the timber sliding through the gaps left by the missing jaws,as there is nothing to stop the wood twisting, apart from friction between the jaws and the wood? Also, if you only have two jaws the wood would only centre in one axis, you would have to manually centre the timber across the face of the jaws.
I may have missed something, and apologies if I am suggesting something you already know, but most turners will hold square stock 'diagonally' between the four jaws. i.e. the corners of the square goes between the gaps of the jaws. This means two jaws are gripping each corner, locking the timber in place.
Take a look half way down this page where it shows that arrangment.
http://www.teknatool.com/products/Chuck_Accessories/50mm.htmI hope that helps but I think most of us are interested to know exactly what you are trying to hold. As Paul Hannaby suggested the best option would be to turn a chucking spigot on the end of the timber, but Steve queried that wouldn't be an option if it has aready been machined to size. And Mark's idea of using angle iron is a good 'home made' idea, albeit not for the faint hearted. Maybe some pictures of the timber in question would help.
