Leather Strap Sizing Question

I'm sure someone knows the answer to this...I'm ordering a strap for my wife...she has a 6.25 wrist and a few suggestions from vendors were

65/105mm and 70/115mm

I'm trying to do this one time (covertly)

Thanks!

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Depends on lug to lug of watch. I went with the short size once (assume they're pretty standard) and there was just enough to tuck into a keeper on my 6.5" wrist with a ~34mm watch.  

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It's a late 60's Omega Seamaster Cosmic...looking for the lug to lug as I do not have it in hand