You don't need to ruin a socket to make a wrench to remove that nut on the cross bolt.
All you need is a piece of six inch (12cm) long x 5mm thick metal/plastic or hard wood and a couple of drill bit buts. Don't use nails, they are to soft. Drill rod will work if you can find the right diameter.
Whatever you decide to use as a wrench handle, drill two holes in it with the proper spacing that will hold the proper diameter pins tightly. Press fit the pins into the wrench handle and you are good to go. Don't make the pins longer than 5-6mm or 1/4 in. If they are to long, to much leverage is provided and the pins will break or bend. This can cause slippage and result in damage to the stock as well as the nut.
The closer to the work you can keep the wrench handle the better.
Just a bit of information on those nuts. Often they have been on the stocks since they were assembled. This means they will be extremely tight and frozen into place. I usually take a punch made of brass, with the center drilled a bit to relieve a space for the end of the protruding bolt. Make sure the punch head is very close to the diameter of the nut.
Place the face of the punch SQUARELY on the face of the nut and give it a sharp whack with a small hammer. NOT TO HARD, use a bit of common sense here.
If you are lucky, the nut will break loose from the bolt. Give it a try with the wrench and see if it will budge. If not, put a SMALL drop of penetrating oil or some other release agent on the nut/bolt and make sure it doesn't run onto the wood. I usually use a bit of sealing wax to prevent this. Of course, rest the stock in a manner that will allow it to be flat so the oil won't run. A friend of mine had a nice method where he uses a bit of penetrant soaked sponge. Seems to work well for him and likely the method I will use next time.
