The general rule is 3/16 for disk brakes and 1/4 for drums.
Depending on the size of stuff that will cnange, like really small drums may have 3/16, and really big disk may have 1/4.
Call inline tube or one of the others and ask what size you need, and what porportioning valve you need.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-