hello rimar2000! i always enjoy your posts they have helped me out on several occasions. so i thought i would offer some help here to pay back the favor.

if the rod is threaded in when the welding is done they distort less. even better if you put some anti-sieze compound on the threads as well.

if a large enough diameter nut and bolt and the correct hardness either grade 8 sae or 12.9 in metric you should be ok. i would look at using a 3/4 inch or 22 mm bolt. fine threads are stronger due to the amount of actuall surface area they provide.

if you can find an old cast vise that has the threads stripped out of it you can use a wirefeed welder to attach a steel nut to the back of the vice. just get it clean and weld a little on each side until it is done all the way around. no preheat needed if you use shoert welds in a cross/star pattern. I know it works as i have done it for a friend and that was sseveral years ago.