1/4" or 5/16" dowel pushrods are fine when put together as Minnflyer shows. You can also cut a strip of covering to replace the shrink tubing and iron on a couple-three wraps if you don't have heat shrink tubing available. The only thing to watch for is the grain of the dowel is straight, otherwise the strength could be comprimised. For smaller lighter models (below 40 sized) 1/4" square balsa works well if firm and also staight-grained.