Screw thread

[Maker]

When you get to small sizes it gets silly. Didn't know it went down to 0.2 incréments.

There's a list of preferred sizes here, though technically you can cut any size thread with that threadform and call it M-whatever-you-want.

 

[Agroshield]

Is it possible that they are not metric, but UNC?

4-40 UNC is 2.85mm major dia., so close to 3mm but the 40 tpi is just over 0.6mm pitch, so would indeed look coarser than 0.5mm.

 

[frank horton]

Note on the smaller sizes u cant beat More and Wright thread gauges.....they are just so much better......

Lost my first set ...grrrrr very expensive.....then when I moved here found em, back o the cupboard....
now have 2 sets....double grrrrrr........hahaha......

 

[Mick Annick]

Is it possible that they are not metric, but UNC?

4-40 UNC is 2.85mm major dia., so close to 3mm but the 40 tpi is just over 0.6mm pitch, so would indeed look coarser than 0.5mm.

Possible but unlikely, Japan has been metric as long as I can remember

 

[Barking Mat]

Photo please @Mick Annick

 

[Agroshield]

There is some talk of M3 x 0.6 here:

Identifying Japanese machine screw - ca 1961

Hi all, I'm, working on an old Rincan table radio with a missing screw. The 3 screws which are present measure... Major diameter 2.9mm (OD) Thread pitch 0.63…

www.antiqueradios.com

and both taps (https://www.chronos.ltd.uk/product/m3-x-0-6-carbon-plug-tap/) and fasteners of this spec. exist (https://www.microfasteners.com/scm3012p6-m3-x-0.6-x-12mm-socket-head-cap-screws-metric-alloy.html).

You might have some luck if you search around the term 'JIS screw thread standard' or similar.

Edit:

A couple of other mentions:

Enya Screws

M3 (0.6mm) x 5mm JIS Pan Head Zinc Machine Screw - COARSE Pitch

Supplier of nuts, bolts, screws. Specialising in obsolete threads types, automotive and stainless fasteners.

www.classicfasteners.com.au

There was metric before ISO metric....

 

[Mick Annick]

Photo please @Mick Annick

Will do, in the morning - now sat in front of the fire with a glass of cremant

 

[Mick Annick]

There is some talk of M3 x 0.6 here:

Identifying Japanese machine screw - ca 1961

Hi all, I'm, working on an old Rincan table radio with a missing screw. The 3 screws which are present measure... Major diameter 2.9mm (OD) Thread pitch 0.63…

www.antiqueradios.com

and both taps (https://www.chronos.ltd.uk/product/m3-x-0-6-carbon-plug-tap/) and fasteners of this spec. exist (https://www.microfasteners.com/scm3012p6-m3-x-0.6-x-12mm-socket-head-cap-screws-metric-alloy.html).

You might have some look if you search around the term 'JIS screw thread standard' or similar.

Thanks!

 

[James1979]

Possibly teaching you to suck eggs, but JIS has a dot next to the screwdriver cross.

 

[Agroshield]

...JIS has a dot next to the screwdriver cross.

JIS is Japanese Industrial Standard. It is analogous to British Standard or DIN or ISO. There is a specific numbered JIS for almost everything industrial. The JIS for screw head geometry is independent from the JIS for thread diameter/pitch relationship. There will be another JIS for A/F size of hexagon fasteners (which is why a lot of M8 Japanese stuff has 12mm A/F).

 

[James1979]

JIS is Japanese Industrial Standard. It is analogous to British Standard or DIN or ISO. There is a specific numbered JIS for almost everything industrial. The JIS for screw head geometry is independent from the JIS for thread diameter/pitch relationship. There will be another JIS for A/F size of hexagon fasteners (which is why a lot of M8 Japanese stuff has 12mm A/F).

It’s a handy way of telling JIS screws at a glance.

 

[Dilkris]

As an eyesight enhancer, lie a rule alongside and take a good, zoomed-in photo with a digital or phone camera and then look at it blown up on a computer screen.

Clever ..... I never thought of that.

 

[Mick Annick]

Photo please @Mick Annick

Forgot to remove a screw to photograph - will do as @Agroshield suggests...

Not apparently JIS

 

[Mick Annick]

It’s the bottom screw I need, top one is a slightly finer thread - straight off the shelf in the local diy shed

 

[Seadog]

Too much light and not enough zoom. Also slightly out of focus. No way of telling what that thread is from the photo.

 

[Mick Annick]

Too much light and not enough zoom. Also slightly out of focus. No way of telling what that thread is from the photo.

I’ll try again - I lost the focus if I zoomed in any more

 

[Mick Annick]

How about this:

 

[daedalusminos]

Japanese metric 3mm diam 0.6mm pitch is a standard

 

[Seadog]

It looks like a 1.25mm. Four threads are taking 5mm.

But nine threads are taking 11mm

 

[rikrobson]

It looks like a 1.25mm. Four threads are taking 5mm.

But nine threads are taking 11mm

the divisions are .5mm not 1mm
looks like .6mm to me, but i'd want to use a pitch gauge to be sure