"Socket head cap screw": https://www.grainger.com/category/so...ecatalog/N-8n7
but that won't get you anywhere at a bike shop. These were special for Shimano, and only, ummm, "experienced" mechanics will know about what trouble they were back in the '80's. The current versions use an 8mm hex key, but a torque wrench is still needed. 30 ft. lbs. is a lot of force to apply with an ordinary hex key (aka "Allen wrench").