There are 2 sizes. One fits EG,EK,DC2 and a few others and the other fits BB6 and a few others.

I had this problem too. I got one to fit my ED civic, and it was too small, so I had to order the one for the prelude and it fits fine.

oh yeah, and when I ordered mine again, it was on back order, took me 2-3 months to get