Never broke a tap before. Just broke two in about 5 mins!

I've had good results using the attached drill size chart, especially for steel.
 

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  • TapDrillSizes.pdf
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That's the one I use also. It states No 7 drill for 1/4-20 for 75% thread. I always use 75% thread unless there's a reason not to since I've never broken a tap before.
 
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