Hello JW,
You listed Ford as a manufacturer of Merlin engines, I suspect you mean Ford of England as Henry Ford refused to build the Merlin in the USA. FOE produced Merlins at Trafford Park, Stretford, near Manchester and total production at Trafford Park was 30,428.
You also listed Continental. Only 6 development engines were made by Continental Motors, whereas Packard produced 55,523.
Graham Kozak's article briefly mentioned the issue of thread sizing.
From
http://www.practicalmachinist.com/vb/antique-machinery-and-history/merlin-engines-rolls-royce-packard-thread-systems-265742/ "An often asked question is; "did Packard replicate the British thread system when they built Rolls-Royce Merlins under license during World War II?" The answer is yes; all threads that were used on the Merlin were accurately replicated by Packard. This would include BSW (British Standard Whitworth), BSF (British Standard Fine), BSP (British Standard Pipe) and BA (British Association)." ..." The job facing Packard when they undertook manufacture of the Merlin was daunting to say the least. It's bad enough having to build a complex product like the Merlin but exacerbating the situation was the fact no tool maker in the U.S. made Whitworth taps or dies. Therefore, Packard were forced into making their own. Although this created a significant hurdle to overcome, the effort was well worth it, Packard and Rolls-Royce components were interchangeable."
BTW, Graham Kozak is a member of Motor City Packards and a volunteer at the PPG. You can read more about this young man here:
https://autoweek.com/authors/graham-kozakThis Post was from: https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?post_id=218946