As is well-known, a great deal of the efficiency of an engine depends on first-class piston rings, and the " Clupet " double-coil, no-gap ring will indicate to keen motorists the care which is now4days expended on this small but important accessory. Made in one piece from centrifugal castings of the best quality cast-iron, the Clupet " piston-ring is claimed to be perfectly gas and oil-tight, owing to its unique construction. A bridge eliminates the gap of the single-coil type, thereby preventing any loss of power at this point, and the double coil automatically adjusts itself to any variation from truth in the cylinder walls, thus retaining the compression and resulting in greater economy in oil and petrol consumption. In the

final operation of grinding the rings on the periphery they are closed right up on a spindle, just as if they were fitted in a cylinder, and ground perfectly round in that position to a limit of .0004 ins. (plus or minus), and also on the sides and between the coils. Even with rings which have been fitted in old engines, after considerable wear has taken place on the cylinder walls, it has been found that they accommodate themselves to the worn condition of the cylinder, giving in some cases an increase in the horse-power of 30 per cent.

The sole manufacturers, Messrs. Clews, Petersen, Piston Ring and Engineering Company, Ltd., of Mill Lane, West Hampstead, N.W.6, owing to the great demand for narrow piston-rings, are now making the " Clupet " piston-rings from 21 mm. or 3/32 in. wide, and all widths above these sizes.