I have to second the comments on the wire saws in most cases. I've only seen two that had any chance of working. One that I've had occasion to use was sold by the Boy Scouts back in the late '70s. It was a solid piece of steel (think heavy gauge wire) that had actual teeth formed on it. I recently found one with similar construction. IIRC it's a bit shorter than the BSA model but it might be that my arms are a lot longer now. Other than these two, if size is a factor, get either one of the folding saws or one of the pocket chain saws.