Grace's Guide is the leading source of historical information on industry and manufacturing in Britain. This web publication contains 147,179 pages of information and 233,417 images on early companies, their products and the people who designed and built them.
of Gunnersbury Avenue, Chiswick, London, W4. Telephone: Chiswick 6444 (4 lines, P.B.X.) Telegraphic Address: "Diamondhart, Chisk, London". (1937)
of Chiswick and Brentford
1905 Company founded.
1934 Became private company.
1937 Electrical switch manufacturers 
1937 British Industries Fair Advert for "Diamond H" Switches and Thermostats. Rotary Switches of all types. "Diamond H" Cooker Switches, flush patterns. "Diamond H" Ironclad Rotary Switch Units. "Diamond H" Perfect Automatic Oven Control. Demonstrations daily with many cookers. "Diamond H" Equipment, various electrical apparatus. (Electricity: Industrial and Domestic - Stand No. Cb.816) 
1937 Electrical switch manufacturers. "Diamond H" Switches. "Diathermo" Thermostats. 
1939 Patent - Improvements in and relating to rotary switches for electric cookers.
1943 Patent - Luminous electric discharge tube or bulb. 
1961 Manufacturers of electrical switches, thermostats, energy regulators and relays. 600 employees