Odd request- Micro metric tap- Kumata

[u18b]

Man, I am stumped.  This is a hail Mary pass to see what happens.

There is a standard Kumata screw (brass locos for Hallmark, Oriental, NJ Brass, etc.

It is the screw that holds the gearboxes and the shell.  It is a pretty standard size.

I'm doing a specialized project and need to tap a hole for those screws- but I have no idea what I need.

As best as I can tell, the outside thread diameter is  .053 inches which = 1.346 mm.

I have no idea what the thread pitch is or what I need to tap these.

Maybe someone with a LOT of specialized tools and a Kumata brass loco could help.


And for the record,  00-90 is just a tiny bit too little  and 00-80 is too big.  Besides, KMT is in Japan- thus I assume these are metric.

[Chris333]

Anything here help:
http://www.newmantools.com/taps/micro.htm

[mmagliaro]

Well, looking at drill and tap charts,...

00-90 drill diam is .889 mm
0-80 is 1.19 mm

If 00-90 is a little small and 0-80 is too big, that brackets your range.

M1.2  x .25 is 0.95mm
M1.4 x .30 is 1.10mm

So, I'd guess it's an M1.2 or M1.4
Can you get an assortment of metric nuts M1.0, M1.2, M1.4, M.1.6  and try your screw in each one?
That's an easy way to know for sure.

[u18b]

Thanks Chris.  I found that site while googling, but I wasn't sure what their numbers meant.

And Max, I sort of felt like it "might" be the sizes you said.  But I just wanted to be sure.

[Ike the BN Freak]

Maybe take it to Lowes or Home Depot, they have those boards with various threads, try to match one of those?

[u18b]

Those do help Ike.  I've used them before.

But these screws are about 1.2 to 1.4 mm.  They are tiny.  Those boards don't go that small.

[fredmoehrle]

Screws usually have a flat on the tips of the threads, and are undersize a bit.
I'd say you have the M1.4 x .30
If you have a magnifying glass or optivisor or some equivalent, you can hold the screw up to a good metric scale and count the threads.
the .30 should have 10 threads in 3mm, the .25 should have 20 threads in 5mm.

[u18b]

I had to use reading glasses AND an optivisor...

But I counted about 10 threads in 3 mm.

So I am going to go with  M1.4 x .3

Thanks to everyone for your help.  This board never ceases to amaze me.

(now if someone could connect me with someone who has a brass Silverliner......)