Need help finding odd screws... (Not even sure the pitch yet)

Working on some odd stuff. I think the screws are proprietary, I just need a few replacements. Due to the small size it's hard to determine what the thread specs are for sure but here is what I can tell you.

4-40 is too big, M3 is too big, 2-56 is too small, M2 is too small, don't have M2.5 to try but M2.5X.45 is very close to 3-56. I was able to run a 3-56 tap into the hole and it seemed to work but was a tad loose but a 3-56 screw will just barely slide through without engaging the threads.

What I am fairly certain of: this is a 56 tpi or .45mm pitch screw

M2.5 is likely too small just like 3-56, but on my tap/thread/drill chart there is a M2.6X.45 listed. I'm somewhat confident that this will give me just enough to engage the threads. This is a low-strength application where I would like to avoid re-tapping if I can (not much material left to tap out).

Problem: I can't find ANY sources for M2.60X.45 screws. Is my chart just outdated and this size isn't used anymore? Anybody know where to get some?

Check out the British B.A. series, - FWIW according to my book, 7BA is 2.6mm OD x 0.48mm pitch.

Limy Sami said:

Check out the British B.A. series, - FWIW according to my book, 7BA is 2.6mm OD x 0.48mm pitch.

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All the charts I'm seeing are showing 2.5mm Major Dia... 6BA is 2.8 mm major but 48 tpi (.53mm)... I don't think that's going to work...

If the item in question was made in GB pre 70 or so dimes to donuts it is BA.

CountryBoy19 : Something I sometimes will do on a threaded hole that is in question, is to turn a piece of wooden dowell to about .020" bigger than the minor dia. of threaded hole to about 3/8ths" long. Screw it in hole by hand and back out. This will give you pitch of threads and minor dia. Good luck.

JH

What exactly are you working on? Many companies, like sewing machine factories, have their own threads.

M2.6 SHCS fasteners are used in some Japanese/Taiwanese linear bearing ball-trucks for fixing whatever you want to move to the ball-truck. They can be found in black alloy, I used to have to buy them for use in some optical gear my company built, within the last 3-4 years. Can't remember who the supplier was, but they are a little tough to find. They are 0.45 pitch, just like standard M2.5 screws.

Here's some starting points:

M2.6 : Metric Screws!, We have the screws you need!
MSPPS2606 - M2.6 x .45 x 6mm - Pan Head Machine Screws - Phillips - Stainless - Micro Fasteners
M2.6 x .45 x 8mm Socket Head Cap Screws A2 Stainless Steel Qty. 20

JohnEvans said:

If the item in question was made in GB pre 70 or so dimes to donuts it is BA.

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Made in 2007.... but I think they wanted to keep the thread pitch odd/proprietary to control supply (for a good reason I admit).

James H Clark said:

CountryBoy19 : Something I sometimes will do on a threaded hole that is in question, is to turn a piece of wooden dowell to about .020" bigger than the minor dia. of threaded hole to about 3/8ths" long. Screw it in hole by hand and back out. This will give you pitch of threads and minor dia. Good luck.

JH

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Great suggestion, thank you! I just did this and after looking at the charts it's looking like a 6BA thread. 47.79 TPI was what I saw on the toothpick that I got to fit in (6BA is 47.85 TPI). The toothpick OD is .103 and just barely engages the threads, I'm estimating major dia. is ~.110 (6BA is .1102). I'm going to try to source some reasonably priced 6BA screws and I will report back.

Thank you for ALL of the helpful suggestions and advice.