what size nuts are on brake porportion valve

i know i need a flared wrench to remove nuts from lines but what size nuts? 69 b body. thanks

Quite likely 5/16"
best to grab a set so that you're covered also for the Master cylinder while you're at it. ;)

Possibly quite different but I just replaced the brake lines on my 67 and the split system block (not sure it's a proportioning valve in 67) had 3 different size nuts on the 5 lines feeding it - I think they were 2 ea-3/8 inch,2ea- 7/16 inch and 1ea-1/2 inch. I may be wrong on the sizes - I was swapping wrenches out so fast I couldn't keep track.