Posts- there is much to learn as in all things ceramic.
I use 2 inch triangles -I would never use any other size but thats me and my situation .
They are from Laguna clay but not what laguna ships normally-you have to ASK for them
Posts come in all different size and I do not mean lengths .
1 inch 1 1/2 inch and 2's are just some of them-that size also is triangle or square
I need stability a car kiln.Tri posts are just such an animal
Bowls fit around them better than square posts for example
I do have some smaller 1 1/2 triangles I use in my electric bisque kiln only as its only 7 cubic feet
1 inch posts are very tippy as Benzine said-I think of them for real small hobby kilns
There are other factors in posts like what temp are you firing to?-what is the fuel?-what is the atmosphere ?
In my salt I use soaps made from kiln bricks as salt is very hard on posts
In my car kiln I use soaps to post over 9 inches or above as they are more stable in a rolling car.
I have some 2 inch square posts when I started out 40 years ago that are still new if anyone wants to trade them for 2 inch triangles as I never use them.
One last note when you fire posts over time at cone 10-11 post will over time compress with the loads-meaning many of my say 5 inch posts are now less than 5 inches .
When I had a slip business many years ago we had a kiln full of 5 1/4 inch pots made to fire a 5 inch tall slip product to cone 10. These posts now are about 5 inches.
You will not see this in 08 temps-I have no experience with cone 6 but would guess firing 5 foot tall loads over time like I do at cone 11 would also compress them.