Does anyone know if anyone still makes the grooved square nuts that the railroads used to hold wood sizing on outside braced cars?

Nut looks like a regular square nut but has a groove cut in one face. Not sure if both sides have groove. At the Ct Eastern RR Museum we have an outside braced boxcar that needs new boards, and I want to get nuts on hand before we start. I would rather purchase them instead of having to mill the slot in 100+ nuts.

Before anyone asks, the groove is not for a cotter pin (otherwise known as a castellated nut), IIRC the groove allows the nut to fold and pinch the bolt, thus preventing loosening due to vibration. Probably the predecessor to the Concave Square lock nut.

Thanks,
Rich C.

These lock nuts were available a couple of years ago. Where I saw them was they were being sold as pole line hardware. If you check with some of the pole line hardware distributors, you should be able to find some. I do know know what sizes they are available. It may only be a couple. I think I have seen 5/16" and 3/8". One caution is that pole line hardware is generally hot dipped galvanized with class three threads. I do not know if you can get them either bright or zinc plate with class two threads.