A pipe coupling for plain end pipe is formed of segments joined end to end surrounding a central space. The segments are connected end to end by lugs on each segment with fasteners extending between them. Each segment has channels on opposite sides that face the central space with floors at different radii. Retainers are received within the channels. The retainers have teeth and one or more offset tabs that cooperate with the channels to prevent improper assembly. A ring seal is received within a channel positioned in each segment between the retainer channels.