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In chokes what does the term 64ths means how does this term derived why not 24 ths or 124ths or 256 ths how did they derive the term for sizing

Hi Dinesh,

I don't know. I must admit that I have never really thought about it and am now wishing I had asked some of the old timers that were around when I “broke out”.

The increase in size is not uniform; it is by 1/64 inch until the 30/64th size and then jumps by two or three 64ths. Since the inch diameter increase is uniform, 1/64, the decimal equivalent is also uniform, 0.157. The flow coefficient does not, this is logarithmic increase and was something easily found on an old fashioned slide rule. This would not tell why 64ths as the same thing would apply to other uniform increments.

Chokes have been around since the 1930’s and the invention of the christmas tree. I would suspect that 64 of an inch was used in order to get good flow adjustment without having too small or too large of pressure changes at each choke change. In other words, trial and error for 64ths as opposed to 32nds and a smaller size would bring in machine shop difficulties as these early chokes would have been made by drilling hole with a bit. Smaller than that would be a fragile bit.

In my profile I state that I will not do someones web search for them but this has me puzzled. After an hour Googleing I found nothing on the subject. I called one of my business partners and he didn't know. I have enclosed a link from an engineering company that shows both positive and adjustable chokes and on page 29 of the 40 page document you can see how the sizes change.  


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Carl Alexander


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