Size of the "truck screw" on Athearn N scale rolling stock

[Mark5]

OK, the word is (supposedly) that the screw is 1.8mm X 3mm - now looking online for this size ...

(no luck so far ...)

[bbussey]

So to understand correctly, the threads are 1.8mm and the length is 3.0mm?

Micro-Mark has gauges to measure, but they might not take the smaller screws into account:
http://www.micromark.com/METRIC-SCREW-CHEKR,7043.html
http://www.micromark.com/GAUGE-FOR-DRILL-BITS-AND-SCREWS,6480.html

Small-Parts carries gauges, but they are expensive.
http://www.smallparts.com/s/ref=sp_search?searchNodeID=16310161&keywords=screw+gauge&x=0&y=0&Action=submit

[Mark5]

Seems kinda self defeating to buy a tool to measure the screw if the goal is to save a few bucks on a screw that Athearn sells for 48 cents a pop.

The length is 3mm, the "size" according to Athearn is 1.8mm. The pitch is coarse.

[bbussey]

According to the site http://www.tribology-abc.com/calculators/metric-iso.htm you take the radius and divide by 0.86603 to get the pitch, which relates to the "M" designation of the screw.



(1.8 diameter / 2) x 0.86603 = 1.039~ Pitch

According to the chart, a pitch of 1.00 is either an M6 or M7 metric screw.  That would mean you're looking for an M6x3.0 or M7x3.0, if I understand and calculated everything correctly.

But as I Google for M6 screws, they look large and I don't see any 3mm in length, so I don't know.

[Robbman]

I don't think that's correct... an M6x3.0 screw would be 6mm in diameter, with a 3mm thread pitch...

If Athearn is saying it's 1.8 with a coarse pitch... it's an M1.8 (coarse pitches are the default... so you don't have to append them)... for the record though, the coarse pitch on a M1.8 is .35mm