PCD, or BCD as it is more normally called, is the diameter of the chain ring bolt placement. there are two main sizes: 110 & 130. Some companies make rings with only one size eg Sugino is 110 and Takagi is 130. That is why your ring does not fit your spider. Other companies like Tuf Neck cater for both sizes in both their discs and their rings. When you buy a ring or spider with only a single set of holes you need to stipulate which PCD/BCD you need to avoid the problem you currently have.