A coupler device is for connecting first and second casings to form a casing assembly with a central axis, each casing having an inner end disposed against the inner end of the other casing such that the casings are spaced along the axis. The coupler device includes at least one generally arcuate connector having a first portion engageable with the first casing and a second portion engageable with the second casing so as to connect the two casings, the connector extending at least partially circumferentially about the casing axis. A retainer is disposeable either generally within or generally about the at least one connector and is configured to prevent radial displacement of the connector with respect to the axis so as to maintain engagement of the connector with the first and second casings.