These spare arms for the S500 Quadcopter frame are extremely stiff and have a super rigid carbon fiber rod through the center making them the strongest arms we have seen to date, will be perfect for you own DIY project.
Length: 210mm (center of motor to end of arm)
Getting those as spare. I dont know if I will ever need them anyway. Can't beat the price.Brilliant product. I have them and I also have some "fake" arms (from different source) with glass fiber rods.Those with carbon have SK sign on them and you can check it by using multimeter. Just put probes in to holes which are on arm - multimeter should beep or show low resistance values (depend on mode of your choice).
Carbon rod arms are more stiff - not so easy to screw or bend them.Quality arms they will break if a motor goes out at 50plus feet though.At this price, I don't mind stocking up on extras. I've never actually snapped an arm, but the brass threaded inserts can strip on a rough landing.