# What would a good tap size be for a 1/4"  pilot hole.



## Marker (Nov 25, 2012)

I am looking for a tap and die set were the hole that you need to drill for the tap is 1/4"   I am sure that there can be more than one size depending on how course the threads are.

    I would like to find one with fairly fine threads.    

   it can't be any bigger than 5/16" after I cut the threads.

   How do you determine the depth of the threads in sae taps?   

   In short....I am looking for something that requires a 1/4" pilot hole that is not too course.


    Thanks


----------



## joefyffe (Nov 25, 2012)

You have managed to confuse the hell out of me!:biggrin::biggrin:


----------



## Marker (Nov 25, 2012)

do you think that a 5/16x 18 will work?    I see in a chart that it calls for a 0.2570" drill 

   It says in the chart...."tap drill size  for 75% .dia"     =  0.2570" dill size.

 also it says........    "tap drill size for 50% .dia"     =   0.2770" drill size.

   Whatever 75% and 50%  means.



   Even though it calls for a drill size of 0.2570"      do you think that I can get away with 0.25"???   I mean it is only seven thousandths of an inch difference?    most drill bits tend to drill a-bit bigger that what it says anyway.



    Joefyffe,     basicly what I am doing is....  

   I have a 1/4" hole drilled in something, and I need to tap it.   I am just trying to fine the right size tap for a 1/4" pilot hole, and a die to match it.


  I have been looking at different tap and drill size charts on the internet, and it seems like none call for a drill size of exactly 1/4"


----------



## mikespenturningz (Nov 25, 2012)

I bet most people use 1/4" drill for that. 7 thousandths isn't much when you are working with wood!


----------



## rherrell (Nov 25, 2012)

A 7mm x 0.75 tap will work, it uses a 6.25mm drill which is .0039" smaller than the hole you have, but it will work. It's also considered a "fine" thread.


----------



## rherrell (Nov 25, 2012)

Chess_Master said:


> do you think that a 5/16x 18 will work? I see in a chart that it calls for a 0.2570" drill
> 
> It says in the chart...."tap drill size for 75% .dia" = 0.2570" dill size.
> 
> ...


----------



## frank123 (Nov 25, 2012)

M7 x .5 will probably work with a .25 drill hole, but if you can get by with a slightly smaller hole and need an inch size tap a 1/4 x 28 would be better.


----------



## KenV (Nov 25, 2012)

Mark --

The better answers will come with a more complete description of what you are tapping.   Coarse vs fine threads are relative to the material being tapped, and loading on the threads.

0.070 is not a big deal in plastics, and is a really big difference in some steels.

Guestimates are pointing to NF, NC, and Metric threads.

So ---what'ca up to?


----------



## KenV (Nov 25, 2012)

Mark --

The better answers will come with a more complete description of what you are tapping.   Coarse vs fine threads are relative to the material being tapped, and loading on the threads.

0.070 is not a big deal in plastics, and is a really big difference in some steels.

Guestimates are pointing to NF, NC, and Metric threads.

So ---what'ca up to?


----------



## Marker (Nov 25, 2012)

I will be tapping 6061 Aluminum at first, and later 303 stainless steel.






KenV said:


> Mark --
> 
> The better answers will come with a more complete description of what you are tapping.   Coarse vs fine threads are relative to the material being tapped, and loading on the threads.
> 
> ...


----------



## Marker (Nov 25, 2012)

Thanks everyone....I have decided to go with a m7x0.5.   I just order 2 sets, one from china, and the other from the U.K.    






frank123 said:


> M7 x .5 will probably work with a .25 drill hole, but if you can get by with a slightly smaller hole and need an inch size tap a 1/4 x 28 would be better.


----------

