UNBRAKO socket cap screws.
"...the Unbrako brand is over 80 years old and remains the socket screw by which all others are measured. Developed in the 1920s, it rapidly became the socket screw of choice for engineers in the US and Britain."

I added this website because sometimes is difficult to find or to choose a good screw of the black type or stainless steel. Best Regards.

• Unbrako