Drill n Tap holes

[Johnny]

Alright, I've been looking at these drill and tap charts and all these numbers are sort of like greek to me. Can someone tell me in regular guy english what size drill bit do I use if I want to tap for a 1/2" bolt, 7/16" bolt and 3/8" bolt?????

Thanks a lot

 

[ruggs]

Alright, I've been looking at these drill and tap charts and all these numbers are sort of like greek to me. Can someone tell me in regular guy english what size drill bit do I use if I want to tap for a 1/2" bolt, 7/16" bolt and 3/8" bolt?????

Thanks a lot

Johnny, This isn't all that dificult and Its something you should try to understand when building a hotrod or most anything, maybe this link will work and then we can move on to understanding the charts.....ruggsMy link

 

[ruggs]

Johnny,
The link appears to work so lets start with a 3/8 bolt.
go down the chart to 3/8.....move across to the pitch or Threads per inch.....move across to the drill size (for fractional bolts it may require a fractional, letter or number bit) Generaly I always tap for 75% thread depth. Try a few practice holes on something,be sure you drill and tap straight and use plenty of tap fluid. clean the tapped hole before you use it........hope It'll help ya .......ruggs

 

[Mr. Fixit]

Alright, I've been looking at these drill and tap charts and all these numbers are sort of like greek to me. Can someone tell me in regular guy english what size drill bit do I use if I want to tap for a 1/2" bolt, 7/16" bolt and 3/8" bolt?????

Thanks a lot

Johnny,

It can be very complicated like anything else one doesn't understand, but here is the simple answer. First you should realize that each of the sizes that you have referenced (as well as all others) can be threaded in a variety of thread counts, but to keep it simple, there is a fine thread and a course thread. As an example, 1/2" x 13 is 1/2" in diameter and 13 threads per inch which is called course threading in that size bolt ot nut, whereas 1/2" x 20 threads per inch is 20 threads per inch, or fine thread. Now to complicate things a bit more, there are drill sizes in fractions of an inch, numbers and letters. To properly thread holes without oversizing them, you should look into a machinist drill set.

Although the bolt diameter is the same, the drill used to prepare the hole is not the same for course and fine threads. The simple answer to your question is 1/2" x 13 = 27/64 drill, 1/2" x 20 = 29/64", 7/16" x 14 = letter U, 7/16" x 20 = 25/64, 3/8" x 16 = letter F, 3/8" x 24 = #1

Good luck..

 

[Youngster]

If you have trouble keeping the tap straight to the hole, weld a nut to a piece of scrap and use it as a guide when cutting your threads.

Ron

 

[estesken]

Also drill size will be identified on the tap.

 

[Johnny]

Alright. Thanks, guys. It's starting to make more sense after looking at the chart a little longer. I'm going go do some practice holes for sure.

 

[17dodgebros]

to keep the tap straight you can also drill a hole the size of the tap example 1/2-13, 1/2 in hole through a block of metal to use as as tap guide. we use this method all the time,it works great

 

[jbisme]

Gotta love whoever came up with using letters, whole numbers, and fractions for drill bits. Good thing for handy charts to convert that mess into decimals.