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For sale is ONE Vulcan EB 32 Eyebolt. It is very large and looks to be 1 1/4" in thread diameter. Maybe metric 32mm thread. Note that it is big enough to be used as a pintle (lunette) hitch for trailers. I verified it by putting it over the 2" ball that is part of my own pickup's pintle hitch.
This is a high quality, USA made eyebolt and I would not hesitate to weld it on a small trailer. You need to consult a qualified safety engineer.