I also have some, what I believe to be kingwood - given to me by his family after the death at 101 of a neighbour cabinet/casemaker - long poles, hard, chocolate/reddish brown with blackish grain lines, way denser than water, also maybe 50mm square and round, 1.5m long, very similar look to yours, maybe finer grain, but is there a further test for positive id? very rot resist - one pole was out in the garden for a washing line, prob for decades - looks almost the same as those kept in his dry attic.