Loose screws.....

[lvrr325]

Anyone know offhand what size the screws are that hold the trucks in on On30 freight cars (Boxcar, flatcar, tank car)?  I need to scare up some that are the same thread but a tad longer, I'll probably need to get some washers to use them since I doubt I'll ever find any with the same heads. 

This because I redid the tank car eliminating the flatcar deck and shortening a leftover frame in it's place.  The result doesn't look bad, same length as the hopper, mine needs walkways, brake wheel and steps added yet, but with a tad longer screw I can even put it back together using the holes  that originally held the tank to the deck.  The bonus is I get another flatcar out of the process. 

[lvrr325]

Wow, nobody?  Screws are usually referred to as a 1-48 or 6-72 or along those lines, that's what I'm looking for. 

[mabloodhound]

LV,
They are probably 2-56 but you can take one of the old ones and measure the outside diameter.
Then compare to this chart http://www.engineersedge.com/screw_threads_chart.htm.
As you see , the OD's are different for each so that should get you there.
If you Google 'screw thread size' as I did there's all sorts of charts, etc.

[lvrr325]

Thanks....  I was just trying to be lazy about it.   I even pulled one out of one of my cabooses to check length...  same length, but it gave me the idea while I was standing there to make a new cupola for it that's the same width as the carbody - which is a huge improvement over the original, it takes the caboose from looking goofy to looking real - even with the circuit board and wiring visible.  I can't think of anything better Bachmann could do to improve that caboose....   

[Jim Banner]

Actually, the truck screws are metric, which is not surprising as they are made in China.  And they are not machine screws - they are self tapping screws.  The diameter is 2.0 millimeters and the thread is about .72 metric pitch, but the thread form is non-standard.

These screws are larger in diameter than a #1-72 but smaller than a #2-56, and much coarser pitch than both.  Replacing them with a #2-56 should work but to avoid the possibility of enlarging or splitting the plastic post with a too large screw with a different thread, you will probably want to tap the holes with a #2-56 tap.  Such taps, complete with a tap drill and a clearance drill, are available from Kadee.  You normally hold these small taps in a pin vice, a tool you probably already have for holding small drill bits.

If you do use #2-56 screws, remember not to over tighten them.  The finer pitch makes it easy to tighten them enough to bulge out the end of the post (king pin) so that the trucks no longer turn easily.

Jim