I ordered a middle chainring (39T) to change on my 105 5703 chainset. I didn't realise until it arrived that it specifies it is for a double chainset. Does this mean it will not fit on the triple? I suppose I could try it and see, but it is still packed so it could be exchanged.
According to the service instructions for the Shimano FC-5703, this crank is a 50D/39D/30T tooth pattern.
The 2 upper rings are "double" with only the 30t identified as a triple ring.
This is not the case with all triple cranks, but with yours, that should be the correct chainring.