CREATE TABLE table_204_828 (id DECIMAL, "whitworth size  ( in ) " DECIMAL, "core diameter  ( in ) " DECIMAL, "threads per inch" DECIMAL, "pitch  ( in ) " DECIMAL, "tapping drill size" TEXT)

how many threads per inch does a 9/16 have ?
SELECT "threads per inch" FROM table_204_828 WHERE "whitworth size (in)" = '9/16'
SELECT "threads per inch" FROM "table_204_828" WHERE "whitworth size (in)" = '9/16'