ASSA ABLOY Fenestration: Experts in the OEM fenestration hardware industry ONE team. Every solution. Interlock USA and Caldwell Manufacturing Company are now ASSA ABLOY Fenestration. Our integrated companies will continue to provide the best hardware solutions for windows, doors and beyond. To do this, we will leverage the combined strength of the people behind two great brands. For more than 135 years, Caldwell has created quality spring balances for window manufacturers around the world. Our products are everywhere from homes to schools, office buildings to hotels, even the United Nations Secretariat Building and the Empire State Building in NYC. It all began in 1888, supplying window products to hardware stores throughout the Northeast of America. At first, Caldwells core product was a clock spring counterbalance that revolutionized the window construction process and firmly established Caldwell in the fenestration industry.