Originally Posted by
mrt2you
with specialized stems,as camilo said, the stem shim fits on the fork square. you don't need angled spacers.
the shims allow the stem to be adjusted at different angles without having to buy new stems. you only have to buy new shims, or just flip it upside down, to change the angles.
with specialized top caps the only reason they are shaped differently is to put pressure on the stem and the shim. with there angled shims the stem is larger and standard top and won't put pressure on the stem. without there top cap in RARE instances the stem can loosten from the shim alowing the bars to twist on the fork.
Just repeating what mr2you said because it explains better what I was trying to say.
To expand a little - the inner diameter of the stem's steer tube clamp (and therefore, probably the outer diameter as well) on is larger than a normal stem. This is because the shims fit inside it and the inner diameter of the shims is what contacts the steer tubes, not the stem itself.
All of the angle adjusting that is done by the shims is
internal, but the bottom and top of the shims are designed so that it doesn't affect the external interface between the stem and the spacers - that remains square. Therefore the spacers used are normal spacers, no angles there.
This also is the reason - like mr2you explained - why the special top cap is needed. The internal diameter of the stem is larger than a normal stem, and therefore a normal top cap won't work properly. There is material between the steer tube and the inner diameter of the stem (the shims). The top cap is different to accommodate this.
So, summary: spacers aren't special, top cap is. Top cap should have been included with stem. If it wasn't you need to return it or get your money back if it was a second-hand private sale. You can check Ebay for the top cap, but it might be a hassle and surprisingly expensive.