A Franklin-type radial buffer provides a rigid connection between a locomotive and tender, allowing no relative movement in the fore-and-aft direction but allowing relative radial movement for negotiating curves.
The diagram of a Franklin radial buffer (below) illustrates the basic principle where two wedges are pressed towards each other by coil springs, forcing the radial buffers (one on the engine and the other on the tender) to maintain contact with one-another through their respective buffing plates.
More detailed information, including a marked-up version of this diagram and photographs of Franklin radial buffers, can be found on Hugh Odom's Ultimate Steam website at http://www.trainweb.org/j.dimech/6167/e1rb.html.
David Wardale specified a Franklin-type radial buffer between the engine and tender of the 5AT in order to use the inertia of the 80 tonne tender to minimize the fore-and-aft "rocking" sensation often experienced with two-cylinder locomotives, this rocking motion being caused by unbalanced inertial forces from the reciprocating masses - viz: pistons, piston rods, crossheads and connecting rod ends.
The amount and position of balance weights on a locomotive's driving wheels are often adjusted to partially offset the horizontal inertial forces resulting in radial imbalance that produces hammer blow which can cause damage to track.
Wardales specification for the 5AT included the requirement that "the engine-tender drawgear shall be of the ‘solid’ (unsprung) type, with a spring-loaded friction-damped intermediate radial buffer (e.g. of the Franklin type), this arrangement giving an engine-tender coupling that allows the mass of the tender to act effectively to reduce fore-and-aft accelerations due to the unbalanced reciprocating masses".