Drill and tap size please?

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bluechrome

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I am wanting to mount a scope using these screws. I don't know what thread they are, but would appreciate if some gunsmith could tell me what drill size and tap size I should use.

They are Torx cap screws.
Threaded width: 4 mm (.1575" or 5/32")
Threaded length: 6 mm with 9 or 10 threads in the 6 mm (.2362" or 15/64")
Head width: 5.75 mm (.2264" or 7/32")
Head thickness: 2.6 mm (.10236" or 7/64")


Thanks in advance
 
Drill size is easy. Nominal Diameter, minus the pitch. It'll get you close enough for anything except NASA contracts.

Tap size? You need a set of thread gages to determine the pitch whether it is a nominally Metric or Inch sized thread, to find the proper tap. Things like the size of the head are not really useful information.

Metric threads are measured from the same points on adjacent threads, as a distance in Millimeters. Inch threads are in threads per inch. Either can be measure with a good ruler, a magnifying glass, and some patience. Example. count out 5 or 10 threads and measure in mm. Divide that measurement by the number of threads measured, for metric, compare the threads to a ruler and see where the threads match the increments exactly, count threads and multiply by whatever fraction of an inch you got an even number in.

Note. A 'Good' ruler, is metal, and likely to be divided into as much as 128ths of an inch, half's of millimeters, and not made of either wood, plastic, or paper.

Oh yeah. Like as not, they are finer threads than you will find in a CTire Tap set or in taps you will be able to buy from other than a specialized supplier of machine tool shop supplies.
 
If you live at or near a large center and you don't have thread gauges any bolt supply house will be able to identify your bolt for you in a second. Then with at least 40 bucks in your pocket head for your nearest machine shop tooling supply shop for the tap (and prob. 6 bucks for a # bit of the required size).
 
Not to dissuade someone from trying new things, but i would be concerned that if you don't own thread guages, you may not own the machinery to do the job properly. Just make sure you research how to do the job, and all that is required. Its easy to cause damage that will cost more to fix than to have had the job done professionally.
 
fingers284 said:
If you live at or near a large center and you don't have thread gauges any bolt supply house will be able to identify your bolt for you in a second. Then with at least 40 bucks in your pocket head for your nearest machine shop tooling supply shop for the tap (and prob. 6 bucks for a # bit of the required size).
Click to expand...

Yeah, and don't forget to consider whether this is a through hole, or a blind hole, and buy the taps you need accordingly. Probably a plug and bottoming taps would do, but a taper tap to start makes life just that much less miserable. Even if it only seems to scratch a bit at the top of the hole, it will guide the next tap in and avoid wallowing out the thread.

And to sorta echo what Fargone4sure said, this sort of question reminds me very much of the discussions about going in to places and being essentially turned away. If you cannot 'speak the language' you probably don't know enough about the work to be doing it.

The basics of being able to speak the language of tapping holes and buying the correct tools to do so, pretty much starts with being able to tell the guy or gal across the counter what size the thread is that you wish to make. When you know that, there are charts and tables almost everywhere that will give you tap-drill sizes, though the formula of nominal diameter minus the pitch is pretty handy. But to be useful to you, you pretty much have to understand the meaning of the words in context here too.
 
Fargone4sure said:
Not to dissuade someone from trying new things, but i would be concerned that if you don't own thread guages, you may not own the machinery to do the job properly. Just make sure you research how to do the job, and all that is required. Its easy to cause damage that will cost more to fix than to have had the job done professionally.
Click to expand...

In North America the vast majority of scope mounts are mounted with either 6x48 screws or 8x40 screws. It would be foolish to use any other screw... and it's easy to cause damage that will cost more to fix than to have had the job done professionally.
 
Fargone4sure said:
Not to dissuade someone from trying new things, but i would be concerned that if you don't own thread guages, you may not own the machinery to do the job properly. Just make sure you research how to do the job, and all that is required. Its easy to cause damage that will cost more to fix than to have had the job done professionally.
Click to expand...

I would agree. No offense OP, but you don’t sound like you have a clue what you’re doing. Take it to someone who does.
 
Fargone4sure said:
Not to dissuade someone from trying new things, but i would be concerned that if you don't own thread guages, you may not own the machinery to do the job properly. Just make sure you research how to do the job, and all that is required. Its easy to cause damage that will cost more to fix than to have had the job done professionally.
Click to expand...

Easy there guy lol, lots of guys myself included have been drilling and tapping things for years without a thread guage. It's only an issue when you need to find a tap to match a fastener you already have, if you need to tap a 6/32 or 8/32 you already know what tap or die you need. I have had a thread guage for a while now and yes it's very useful but it has no bearing on someone's skill level lol.
 
I see OP has fitted the scope so this is after the fact.

I was going to suggest abandoning the 2 or 4 screws he had in his possession, and go to (say) some bolts supply and purchase, as a set, machine screws with known thread pattern, a couple of appropriate drills, a taper tap and a bottoming tap of the same thread pattern, some tapping fluid, and some spares.. Then to practice drilling and tapping prior to attempting it on the rifle.

Bust a tap inside a hole and you're in a heap of hurt - solvable, but it can be ugly.
 
AikiNut said:
I see OP has fitted the scope so this is after the fact.

I was going to suggest abandoning the 2 or 4 screws he had in his possession, and go to (say) some bolts supply and purchase, as a set, machine screws with known thread pattern, a couple of appropriate drills, a taper tap and a bottoming tap of the same thread pattern, some tapping fluid, and some spares.. Then to practice drilling and tapping prior to attempting it on the rifle.

Bust a tap inside a hole and you're in a heap of hurt - solvable, but it can be ugly.
Click to expand...


Like minds........
That is exactly what I did.
Thanks.
 
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