The picture above is the excellent replica Clapp-Eastham spark key SN: 20 completed in 1993 on a marble base by K.Vanslette from Hattiesburg, MS(I think he has moved to Florida since). A very well machined key anyone would greatly appreciate. Solid feel and real good appearance. The dimensions of the marble base are: 6 inches(151mm) long by 3 1/2 inches(87mm) wide by 13/16 inch(20mm) thick. The overall key length to outer front edge of the knob is about 7 3/4 inches(197mm). the key weighs about 2 pounds 3 ounces(550mg). A green felt covers the bottom of the base for a smooth setting on the operating bench or desk/table.
This is the real CLAPP-EASTHAM "BOSTON KEY" on a black ebonite or bakelite base found at Dayton, Ohio 2006. It has the same base dimensions as the key above but lighter weight. Always a good reliable key with sturdy construction from long ago.
This third photo is of the Bowman spark key without any markings on a nice heavy marble base. Made by Bowman and provided by them to Sears, Wards, perhaps some other stores long ago for them to sell. A very solid key, large contacts, good feel when sending, and definitely a heavy key.