Service wrenches have been made by a number of companies over the years, Bonney, Armstrong, Wright, Proto, Martin. The Martin ones may be the Spanish made ones, the others are US made. These are made for thin nuts used on hydraulic fittings, and other areas where a thin wrench is needed. Do not apply lots of torque, they will spread. Great however for running something that is too tight to run by hand, as they are short and will let you run the threads all the way down. Then you can use something else to make it tight.
Charles