1. The method of marking British thread sizes is determined by two parameters: the thread diameter and the thread pitch per inch.2. The thread diameter is typically denoted by a capital letter D, while the thread pitch is represented by the acronym TPI (Threads Per Inch).3. In the marking process, the thread diameter and pitch are enclosed within a dotted circle, and the corresponding numerical values are specified within this circle.4. The diameter of the thread is measured in inches and examples of notation include 1/4", 1/2", and 3/4". This measurement refers to the external diameter of the thread, which is the distance between two corresponding points on the helix.5. The thread pitch per inch indicates the spacing between adjacent threads on the螺旋線. A higher pitch value corresponds to a wider spacing between threads.6. The notation is typically supplemented with a slash symbol (/) above or below the right side of the thread size to indicate that it is a thread dimension.In summary, the method of marking British threads involves indicating the thread diameter and pitch per inch. The diameter is measured in inches, while the pitch is expressed in TPI. The thread diameter and pitch are marked within a dotted circle, with the numerical values specified inside the circle.