What type of freeze plug

What type of freeze plug goes in the hole on the back of the head. I currently have the type that is a big rubber disk sandwiched between two metal disks with a hex head bolt on one side. I have read that this is only a temporary fix. What should I be looking for in the correct plug? What does it look like? Autozone had some that were more of a cup shape that had to be hammered in place. What is OEM?

Yes I searched and could't find exactly what I was looking for.

1996 4.0 auto 4wd sport

OEM is the "cup style" plug that you drive in place. Use a socket that just fits inside the cup, and drive it until the upper edge is 1/16" to 1/8" below the surface of the cast boss for the plug.

Welch plugs can usually be had in either stainless or brass - but I've noticed that it's not a very good grade of stainless. I prefer brass.

You are correct that the rubber "sandwich" plug is a temporary fix - and if you don't know how long it's been in there, it's very temporary! I don't think I've ever run one longer than a fortnight...

Happen to know what size that is? I am thinking 2 inch. Also, how difficult is this without removing the head?

Not sure - but there are standard sizes, and most of them can be measured with a tape.

If it's the one on the back of the head, you can probably service it in situ if you get a little creative. Otherwise, you're pulling the head.

Just for others who may read this. I had the rubber type in, drove it for about 1500 miles, and it blew out. I already had another rubber type, so I went to put it in for a temp fix (I did not do the first one). As I was working, I discovered that these really don't fit. They are too thick. They can't be seated properly, due tho hitting something inside the head. Save yourself time and trouble and don't even bother with the rubber type.

FWIW