They're polystyrene and come on sprues of 4, and you get 100 for $22. The edges are beveled so they fit tightly against a 25mm base, leaving no gap on the surface of the base.
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| Left to Right: Adapter Ring, Adapter Ring on 25 mm Base, 32 mm Base |
They fit quite well on a clean base, though I've found that a thick coat of paint on the edge of the base causes a gap where the halves of the ring come together. Fortunately, the gaps aren't too noticeable and are mostly covered by another coat of paint.
The rings turn a 25mm base into an excellent approximation of a 32mm base, though they are a bit lower. This is because 25mm bases are a bit lower than 32mm bases, and these rings lack a layer of plastic to underlie the 25mm base and raise it to the appropriate height. As a side effect of this, I've found that the ring tends to ride up on the base a bit as the glue dries. This isn't a problem if you keep an eye on it, but it's something to keep in mind. If this would bother you, the conversion rings from Tabletop Adapter have the necessary bottom layer, though they cost a bit more.
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| The model on the left has an adapter ring while the model on the right is based on a 32 mm base. |
Basing the models with painted sand goes a long way to covering any gaps and unevenness that may have snuck in as the glue dried, as well as obscuring the difference in height.
In the end, I'm really happy with the Eccentric Miniature conversion rings. I'll admit that they're not the best design due to the issues mentioned, but they do a good job for an excellent price. If you want to rebase a large Marine army, they provide an economical way to do it.