The popularity of Flat Head Cap Screws grows because of its positive, hex-socket wrenching feature, use of heat-treated alloy steel and precision Class 3 fit threads. Non-Slip Driving: With the close-fitting, internally engaging hex key, power is transmitted for extra firm setups without loss through side play, reaming or slipping. Costly slips of the driving tool are avoided, along with possible damage both to the work and the screw.