Hi. I want to check whether these hinges are real brass or whether they are plated? Also, it is a bit of an experiment to see if these will work in my application (a decking hatch with very specific dimension to the fixing screws being 61mm from the top surface) so should I buy one to try and then order the remaining 5 which must be visually the same OR do you have a returns policy that would allow me to buy all six up front and return (in unused condition) if not suitable?