Just to join in the conversation,
My 65 Paramount serial # V-36 has the ½ (or 12.6mm) seat stays measured by with an old set of Starrett dial calipers by hands that have made their living doing just that from the depth of fuel in a nitro drum to the thrust clearance on the reactor coolant pumps at Diablo Canyon.
Not that I cant be off by a few thou!
Beers & Cheers!
Scott Mattern