Tap and Drill size

[rodmkr]

I am working on a project using a Leupold Scope.
I need to find out what size and thread the target knob hold down screws are.
My screw measurement gear does not go that small and I need to find out so I can purchase a tap and drills.
I think they are 4/40 but need to find out for sure.


rodmkr

 

[extropic]

I didn't see any question marks in the OP but . . . maybe it's time to invest in a proper thread gauge.

Actually, one for inch (TPI) and one for metric (mm pitch) would serve you for a lifetime.

 

[wawoodman]

If you think it's a 4-40, and don't have any other way to measure, is there a hardware store nearby where you could buy a 4-40 machine screw, and try it?

I believe you should check the size on the project in front of you, rather than relying on catalogue data, or other peoples' experience. Stuff changes. (Just my opinion.)

 

[wawoodman]

Nobody can answer the question, without having the goods in front of them. What if we said, "Yes, it's a 4-40." The OP goes out and spends what, $10? And then we find that the factory or someone else changed it to 2-56 or 6-32?

It's our fault?

Someone with 60 years of experience should know better than me, how things can change.

Just my opinion, of course.

 

[HMF]

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[francist]

Hey rodmkr,

I bought a couple of these years ago on a whim -- and I'm surprised how much I've used them! Thread pitch sets are great and I have those too, but these type are really handy to use for the tiny fasteners. Not expensive, and there's both imperial and metric versions. This is the brand I have, but there may be others just as good too.

-frank

 

[mikey]

I am working on a project using a Leupold Scope.
I need to find out what size and thread the target knob hold down screws are.
My screw measurement gear does not go that small and I need to find out so I can purchase a tap and drills.
I think they are 4/40 but need to find out for sure.

Rodmkr, the simplest way to be sure is to use your calipers and measure the OD of the screw. Compare that to the nominal size in a chart you can find anywhere on the net; it will not be exact and your screw will probably be a bit smaller but it will be close. Once you know what the nominal screw size is likely to be, use a thread gage to check the thread pitch or measure it with a rule to get threads/inch.

If you don't have calipers and a thread pitch gage then buy some; you'll need them. In the meantime, the next best option is to take the screw to the hardware store and start checking fits of nuts. Keep in mind that a hardware store nut will be a bit loose but it will at least tell you what you have. Then you can order your taps.

 

[682bear]

Bear in mind that, like many gun screws, it may not be a standard thread pitch for the particular major diameter. In other words, you may have to purchase a specialty tap...