US Patent 7837584 Chain

A chain includes a connecting unit including two chain plates, and a link unit having first and second link plates parallel to the chain plates and a link pin. The first link plate is formed with a stop block and a retaining hole having an insert hole portion and a retaining hole portion. The link pin has an engaging end portion extending through the chain plates and the retaining hole portion. The connecting unit is pivotable about the link pin between a first position, where the link pin is allowed to move entirely from the retaining hole portion into the insert hole portion to thereby allow removal of the link pin from the first link plate, and a second position, where the link pin is not allowed to move entirely from the retaining hole portion into the insert hole portion due to contact of an edge of one of the chain plates with the stop block.