M5A 'bottlecap'. 3.6 RPM, pretty easy to rebuild, closing the aluminum case after opening isn't so easy. Fortunately the field and coil assy holds the case closed tightly against the plate when assembled. I glue the alloy cap to the capsule base lightly first to contain the lubrication. I retrofitted a Telechron H type long ago with the M5A pinion as a experiment, and it worked fine. I guessed the torque requirements of driving this movement over years would shorten the life of a H type, but never encountered that in use.