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Drafting: Tapping & Clearance Hole Information


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I am not sure what size tap hole I should use for a 9/32 clearance hole. Can anyone tell me what tap hole size I should use?

 

I would also appreciate any recommendations on a good website to learn more about Tapping & Clearance Hole Information.

 

Thank you in advance.

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As a rule of thumb I've always considered a clearance of 1/32 for screws from 1/4 up to 7/16. 1/16 for larger. BTW you reference a "Tap hole size" so I'm merely stating screw size. The tap drill is dependent upon the thread pitch along with other factors.

 

 

So if your clearance hole is 9/32 then that would work well for a 1/4 screw.

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This is an invaluable little reference booklet for tapping/clearance hole sizes along with other workshop data.

http://www.stationaryengineparts.com/Zeus-Precision-Data-Charts-and-Reference-Tables.html

 

Don't worry that it says metric edition on the cover, there is imperial thread data (anf, anc, bsf, bsw,etc) in there as well.

Every draughtsman I have ever worked with has his own copy.

 

P.S. Check your local bookstore, they may have it at a lower price.

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A tapped hole and clearance hole are two entirely different things. A tapped hole is one that is large enough for the screw shaft diameter to fit through but small enough to have enough thread engagement when tapped. What is the thread specification that you're trying to use.

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