Rigidity of a futon bed mattress is more important when the futon is being used mainly as a sofa. Flexibility basically defines how easy folding the futon mattress is going to be. If you are going to folding the mattress daily from sofa to bed back to sofa again, then buying a futon bed mattress with a lot of flexibility makes sense. Futon bed mattresses are made from a variety of materials.
The hinges were attached to the arms of the futon frames with two bolts and two nuts. While this design was OK the hinges themselves would fail when too much weight was applied to one side or the other. These would also bend out rendering them useless in the operation of the futon. Most specialty futon retailers pay little to no attention to black metal futon frames. Retailers Ive spoken to have said that the black metal futon frame is the number one service headache when it came to futons with over 95% of service issues being the failure of a black metal frame component.
Early designs involved a steel tooth design that would fit into pocket welds on the arms. These would snap off over use. The alternative design was to run a bolt through the arms and into the rails. While better it still did not address the issue of bending stretcher rails. Bent hinges also added another issue that would happen from use over time. While not as common as the other problems this issue still led to the failure of many black metal frames.
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