Proudly Made in the USA, the Rectangular Current Transformer Model RT3737 or 1000:1 transformer are fully encapsulated for indoor and outdoor applications. It's rectangular design with a window diameter of 3.7" x 4.7" and a standard 1-amp secondary. Others available. The RT3737 terminals are brass number 10-32 UNC. CSA Optional. This model weighs in at approximately 5 lbs.