you can go small or med...small will be more fitted and good over a t-shirt and probably a base. i think a midlayer might max it out if you measure 39-40 with a tape as the small pit to pit is 21"x 2 or 42", you might get a fleece bross type thickness under it.... i would just buy 2 since u are borderline (lol just kidding) but seriously i am using both a med and a large for different situations.....
isnt that just wild??
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