i just got to know what everyone thinks they are. i always thought a limited slip was a posi, but some people that ive talked to think it is an open diff. am i right or are they right?[img]i/expressions/face-icon-small-confused.gif[/img]

 

You are.

There are many different types of rearends. A spool is just a piece of metal that the axels index into. With a spool there is no diferential action at all. Some people call them a locked or solid axel.
The next step down is the locker. These have teeth that will index into each other and lock the two sides together; solid.
The next step below that is a clutched type of rearend. Gm's version is called a posi-trac. All different brands have there own "special "names. All the ones I have seen have some type of friction material in them. Some have cones, some have plates. They all work about the same. They load the side gears so they won't spin as easy.
The next step down is the open differential. There is no load on the side gears and they both can spin easy independent of each other.

With all the above types there are sub-categories. Like there are "air lockers" and "spring lockers". There are mini spools and full spools, ect. You get the point. There is also new stuff out on the market each year. I think Honda has a new way to do this with some sort of a weird gear deal?