M3 fine metric 0.35 thread screws/bolts

[Hsing-ee]

Just doing some more experiments, I have bought a set of taps for this spec but have found a UK or even European supplier of bolts or screws non existent.
I have some on order from China but this will take some weeks.
Anyone know where you can buy these?
People who sold me the tap said it was an odd size (after they sold me it) and went on to say Metric fine is unusual under M8.
Standard thread size is 0.5 for M3.
It is for fitting a scope ramp to an old air-rifle. Glue plus screws.

[Shed tuner]

That is really fine... how much thread depth have you got ?

Is it just a cosmetic repair ? Assume it's a springer ? If so, I'd not like to mount a scope to something secured by such a weak thread. Maybe retap and go up to M4 or ideally M5 if you do want to actually use it ?

[Hsing-ee]

That is really fine... how much thread depth have you got ?

Is it just a cosmetic repair ? Assume it's a springer ? If so, I'd not like to mount a scope to something secured by such a weak thread. Maybe retap and go up to M4 or ideally M5 if you do want to actually use it ?

I thought it would be better getting some more turns in there .. but you know this kind of stuff better so I will just go M5.

[Shed tuner]

I thought it would be better getting some more turns in there .. but you know this kind of stuff better so I will just go M5.

M4 x 0.5 might be fine. Thread depth is key. If the rail is significantly thicker than the cylinder you are mounting it to, you could consider bolting up from underneath, threads cut in the rail ? Obv you'd need to countersink the bolt heads to avoid fouling the piston skirt.

[Born Again]

A possible source for very small bolts/screws is an old hard disk drive. They're usually properly threaded, not the tri-lobular self tapping types.

[angrybear]

That sounds suspiciously like a 4BA to me
Where was the 'old air rifle' made ? only mainland Europe used metric pre 1970's.

[KWK1]

The old standard is 3 threads in the work.

[Shed tuner]

The old standard is 3 threads in the work.

I recall a 1.5X the diameter rule...

[ggggr]

I think the thread of the ones on the little ramp on the DIana 25 (British guns) was 4Ba. The trouble you have is you only have the thickness of the cylinder to go into and it is curved! . I think they only went in 3 or so threads and a fraction too long and they would foul the piston. I've a feeling that why Bsa Meteor pistons (Mk5?) and Scorpion pistons had a slot in them so the rearsight screws wouldn't foul.

Many years ago in AGW a bloke did an article about silver soldering a ramp to a Webley Mk3.

Baz reckons Tiger seal is good for fixing a ramp and will come off when you want it to, without removing blueing.

I'd give that a go rather than trying screws.

[Brad3]

The 0.35 is unusual because normally speaking you would not call for fine pitch below 4mm.
You are correct it packs in more threads and often used by Walther for that reason, and for fine adjust threads on sights but 3mm too small. They use M4 and M5 fine.
Your problem then is finding screws.
A good possible source is Chambers for old German gun sights.

[Hsing-ee]

Baz reckons Tiger seal is good for fixing a ramp and will come off when you want it to, without removing blueing.

I'd give that a go rather than trying screws.

I was going to use epoxy AND screws but all options are on the table. The screws would be to help stabilise the ramp horizontally rather than vertically, which if I think about it, could be achieved by simple pins/pegs.

[Hsing-ee]

A possible source for very small bolts/screws is an old hard disk drive. They're usually properly threaded, not the tri-lobular self tapping types.

I think you are right these are the only M3 ones with that thread size ...

[Hsing-ee]

That sounds suspiciously like a 4BA to me
Where was the 'old air rifle' made ? only mainland Europe used metric pre 1970's.

It was the thread chosen by me in my ignorance, so now I have set of taps but no bolts because they dont make them! apart from maybe these chinese ones or the computer cannibalisation stuff...

[Brad3]

It was the thread chosen by me in my ignorance, so now I have set of taps but no bolts because they dont make them! apart from maybe these chinese ones or the computer cannibalisation stuff...

He's right with the 4 BA.
Your wanting to thread the thin wall of a cylinder and used good thinking in going for fine thread in attempt to try and get maybe 3 or 4 threads into the slim wall which I've also done.
You can find M4 fine taps on Amazon for a few quid.
I've also run an M4 fine die down regular M4screws with decent results.
Both metric fine die and taps available on Amazon for hardly any outlay.

[angrybear]

It was the thread chosen by me in my ignorance, so now I have set of taps but no bolts because they dont make them! apart from maybe these chinese ones or the computer cannibalisation stuff...

So what !
if they're 4BA holes use 4BA bolts, send the taps back (or keep 'em but they sound pretty useless).