A/C heater core o-ring size?

[Ranman69SE]

Does anyone happen to know the exact size of the o-rings that seal between the heater core and feed tubes on an AC car (1969)??  Or, who might carry them?  I purchased new rings at a local hardware store that I think are close, but they seem like they may be a bit too small as the pipes go on pretty easily (I have not yet pressure tested it to see if they seal).  I know DMT sells a complete rebuild kit, but I really just need the correct o-rings, and I really don't want this thing to leak once installed 

[PlainfieldCharger]

Just received that DMT kit. Measured up those o rings. OD 11/16    ID 9/16  Remeber to buy the nitrile rings. Why they had so many possible connections and possible fail points :shruggy:Just seems it could have been different.

[Ranman69SE]

Thanks!  I was just about to ask you how thick the rubber is, then the two remaining brain cells I have decided to get together and help me realize that if I subtract the i.d. from the o.d., then divide by two.........voila!