US Hobbies Bolster

[up148]

I purchased a small bag of these at a March Meet back in the late 90's. The bag was marked US Hobbies by the seller and I later confirmed this was true. Installed a pair on an Atlas 8000 gallon tank car 10-15 years ago but never finished the project and trying to find the correct screws to fit it. I don't know if its SAE or mm threads, but know it takes a screw smaller than 4 mm as I checked that today.

The photos don't show it, but there is a threaded brass insert cast into the bolster.

Any thoughts?

US Hobbies Bolster 004.JPG (149.97 KiB) Viewed 4410 times

US Hobbies Bolster 005.JPG (146.61 KiB) Viewed 4410 times

US Hobbies Bolster 006.JPG (142.54 KiB) Viewed 4410 times

[R.K. Maroon]

I have one in my hand and it takes a 4-40. I have no idea if they were all that way.

[R.K. Maroon]

But wait....I found a PSC version and it takes a 3 mm. All bets are off.

[Rufus T. Firefly]

3mm is what I seem to remember. Doesn't matter to me; I use drill and tap for 4/40 for everything as a standard so I'm not bothering looking for where the 23 other sizes of screw are in my shop.

[up148]

Thanks guys, these must be the 3 mm version as I have some 4-40 screws and they don't fit. So, Rufus, can I just drill and tap the existing brass insert for 4-40? Standardized works for me.

[ScaleCraft]

I don't even think you have to drill.
The actual diameter of an M3 screw is usually about 2.9mm.
A 4-40 diameter is 2.845 mm. According to he algore.

I have found that ain't exactly right, but I have done a whole lot of 3mm to 4-40 conversions, never drilled, just tapped with a t-bar. Turn once, back out, another turn, back out. Clears the chips.

The trick is, especially if the screw head is designed to fit for truck alignment into the truck bolster, is to use a drill press (no power) use the chuck key or pull the bar out of the t-bar and chuck that up.

Usually I am good to go by eyeballing the t-bar and tap (look at it, then look at 90 degrees).

[up148]

I'll have to eyeball as no drill press.

[Rufus T. Firefly]

I'll have to eyeball as no drill press.

I'd just run the tap in and go with it.

[bob turner]

Be sure to let me know if you need more of them.

[up148]

Not sure Bob. I have maybe 7-8 pairs and so far modifying them to fit an Atlas tank car (no factory bolster) took a lot of changes and its still not right....going to try and make it right. Not sure exactly where I would use more but appreciate the offer.

When and why were these originally produced? I've never seen any on any USH car I own(ed) and haven't seen them on any PSC car either.

If I purchased these in the mid 90's, at a swap meet, I have to figure they were produced before that.

[up148]

Turns out the inserts were already 4-40 thread, I just didn't have any 4-40 screws. Bought a tap set (needed it anyway) and clean out the threads.