Re: Duncan designed JB/Jazz
First, look at the back plates to be sure they are the model that your guitar specs' tell. My jackson came with two HB-103 (Designed Distortions) instead 102-103.
Second: I bought a Distortion set to replace them. THEY WERE NOT TWO DISTORTIONS MADE FOR A KOREAN FOLLOWING THE SAME SPECS AS THE ORIGINALS. They are tiny!!! They also weights like a half. Its magnetic force is weaker than the stock cheap LTD ones. Sorry but Duncan has made a mistake with these things.
Go for nice ones.