Some metal -to- metal clamp on items damage steel tubing and/or the paint (eg. the frame) when attached and tightened. I've just removed a number of fridge magnets from a metal cabinet and note that they are thin, plastic coated and bend so you can wrap them around tubing. In some cases this may be a useful inexpensive way of protection for your frame. Fridge magnets may also in some cases be a useful way of reducing a gap so that you can get more effective clamping. Just a thought.