Heres from the Diamond chain FAQ describing master links, sounds like you have a press-fit side plate:
Slip-fit, the most common and most popular, are provided for general chain applications and allow the easy slip fit assembly of the cover plate over the pin ends. This slip fit construction does not have the same integrity found in the assembled chain and can reduce the chain's working load capacity by as much as 30%.
Press-fit connecting links are provided when the integrity of the connecting link needs to be equal to that of the base chain. This design utilizes pitch holes in the cover plate that are smaller than the chain pins, requiring the user to press the cover plate onto the pins before installing the spring clip or cotter. While more difficult to install this type of connection provides the greatest load carrying capability.