I have a 91 nissan 4x4 the front studs broke off and iwas trying to replce them but the axel nut is on bt i cant find a socket anywhere to get it off

need to remove axel nut or if hub bearing retaining bolts

Measure it with a metric ruler from one side of nut to the other. It will be in millimeters, anywhere from 27mm to 32mm, most likely.

If it is just one stud,it's best to leave it be,I have a 85 Nissan 4x4 and one stud is stripped and I have a repair manual and with it being a 4x4,there is a lot of parts to be remove to get to the stud and it may effect my 4x4ing if something doesn't go back just right.I found a repair guide for yours but it doesn't go into detail.It's best to have a repair manual for this so you will know how everything goes back.

Depending on if its a rear axel or a front rotor how you're going to do it is different. The method is still the same though.

The studs just have a serrated edge right under the head that holds them in place. They just need to be smacked out with a sledge hammer and the new stud came be pulled back in with a good lug nut and some washers that the studs will fit through without binding.

For instance,
A front rotor would need to be pulled off the vehicle. Looking at the back side you can see the head of the stud. Place the rotor on a firm surface and hit the stud from the side that is broken to drive it out through the back side.
Put the new stud in from the back side. Try to turn it to where it feels like the grooves (serated area)on the stud are locked into the grooves on the rotor. Then put some large washers over the threads (so if there is a shoulder on the stud that comes through the nut will not bottom on it). Put the nut on and tighten it do bring the stud through.

Some hubs have a sweet spot to change the studs If not you'll have to press out the bearing by removing the tie rod,ball joint, axel, strut and breaks then take the hub to someone with a press.

The front axel is a two piece assy. remove the 4wd
shift moter from the axel housing. Once the moter
and fork are off , remove outer axel.To remove inner
axel, remove differential cover and let it drain.
There is a C clip on the axel, remove it and work the
axel out through the axel tube.(if it is broken)
To remove the rear axel. Remove diff. cover and drain.
Remove the pinion lock nut(or spring clip) and slide
back pinion shaft. Remove retaining clip from axel
and remove axel. To remove broken piece I use to
use a length of an old whip antenna, to push it out.
If you can find a piece of heavy gauge wire to push
it out.(a plumbers snake may work)Also only have
one axel at a time out of either housing, this will
make it easier to reinstall the axels.
I hope I was of some help. Good luck.

you may need a deep socket. I belive the size be 30 or32 mm

the hub is seized into stering knuckle..you can try putting a socket or a small 1/2" drive extension between 1 ear of front axle shaft and axle housing and turning wheels all the way to whatever side you have socket in..this will push hub out of knuckle..try doing this both ways with engine running..keep axle nut on shaft

They should be replaceable w/o pulling the axle. Imagine a common nail; you have the shank of the nail with its point and the flat head on the other end. Your lug stud looks a little like that except the part that comes through the axle flange. It is a little larger than the threaded part and has "lateral lines" machined into it to grip inside the flange. Otherwise it would spin either way when you tried to tighten or remove it. To get the broken ones out, use a high quality flat end punch and a hammer to drive them backwards (toward the center of your differential) and eventually out of the flange. Look for the area that will give you the most room so they will not hit aything while they are backe out of the flange. The new studs can be installed in the reverse manner. When you get them just barely started through the flange, use your fingers to twist them back and forth to "feel" for the grooves where the old stud was seated. Once you get it barely started in the grooves, grease the threads, slip an old 1/2 inch drive socket over the new stud (make sure it doesn't fit tight) slip on a thick flat washer or 2--3 thin ones, turn your lug nut around backwards so the tapered end faces out and begin to tighten it. Go slow, make sure the new stud pulls through the flange evenly. Take the nut, washers and socket off every now and then and look at your progress. When the back side of the stud is seated on the back of the flange, you're finished. Now, always grease the studs. ALL OF THEM, EVERY WHEEL. The monkeys that put on tires these days use impact wrenches and if you just have to let them do it, grease will help you loosen the nut if you have to and it will help prevent future failures. A DRY stud and nut causes a twisting motion to take place in the body of the stud when its tightened. This leads to premature metal fatigue.

I dont think you have to remove the nut that just frees the cv axle. The rotor is probably rusted on give it a few good hits with a hammer on the front where studs are do not hit brake surface it should free up